Notebookcheck

Asus ZenBook S UX391U (Core i7, FHD) Laptop Review

13.3-inch lightweight. The ZenBook S (UX391) is a particularly light 13.3-inch laptop from Asus. It tips the scale at just 1 kg, but the manufacturer says the performance is not affected. We review the rival for the XPS 13.

Asus announced its new ZenBook S (UX391) back at Computex. The focus of the new ZenBook is mobility with its slim construction and a weight at around one kilogram. However, the device also features Intel's latest quad-core ULV chips for increased performance. The manufacturer utilizes a so-called ErgoLift hinge for improved airflow and cooling. The base unit is tilted by 5.5 degrees when you open the lid, which improves the typing experience, airflow, and the sound quality as well.

Besides two 8th generation Intel processors (Core i5-8250U & Core i7-8550U) and different memory options, you can choose between three different 13.3-inch displays. There are two 1080p screens (matte or glossy), even though the glossy option is not a touchscreen. Asus advertises full AdobeRGB gamut, but this should be limited for the optional glossy 4k touchscreen.

Prices for the Asus ZenBook S UX391 start at 1099 Euros (~$1279). Our test model (UX391UA-EG023T) retails for 1349 Euros (~$1570) and features a matte 1080p display, the Core i7-8550U, 8 GB RAM, and a 512 GB PCIe-NVMe-SSD.

The biggest rival for the Asus ZenBook S is definitely the current Dell XPS 13 we already reviewed a while ago. The XPS 13 is not available with a matte panel anymore, so we are eager to find out whether the ZenBook S is a serious alternative. We also include other comparison devices like the Huawei MateBook X or the MateBook X Pro (if you need more GPU power), the HP Spectre 13, and the Apple MacBook Pro 13 (without Touch Bar).

Asus ZenBook S UX391U
Graphics adapter
Intel UHD Graphics 620, Core: 1150 MHz, Memory: 1066 MHz, 23.20.16.4927
Memory
8192 MB 
, LPDDR3-2133, soldered
Display
13.3 inch 16:9, 1920 x 1080 pixel 166 PPI, AUO B133HAN04.9, IPS, glossy: no
Mainboard
Intel Kaby Lake-U iHDCP 2.2 Premium PCH
Storage
Samsung PM961 NVMe MZVLW512HMJP, 512 GB 
, 455 GB free
Soundcard
Intel Kaby Lake-U/Y PCH - High Definition Audio
Connections
1 USB 3.0 / 3.1 Gen1, 2 USB 3.1 Gen2, 2 Thunderbolt, 3 DisplayPort, Audio Connections: 3.5 mm headset, 1 Fingerprint Reader
Networking
Intel Dual Band Wireless-AC 8265 (a/b/g/n/ac), Bluetooth 4.2
Size
height x width x depth (in mm): 12.9 x 311 x 213 ( = 0.51 x 12.24 x 8.39 in)
Battery
50 Wh Lithium-Polymer, 4 cells, Battery runtime (according to manufacturer): 13.5 h
Operating System
Microsoft Windows 10 Home 64 Bit
Camera
Webcam: HD-Webcam
Additional features
Speakers: Stereo Harman Kardon, Asus SonicMaster Premium Audio System, Keyboard: Chiclet, Keyboard Light: yes, 65W PSU, Asus Mini Dock, Sleeve, McAfee Live Safe (trial), Office 365 (trial), Asus Tools, 12 Months Warranty
Weight
1.018 kg ( = 35.91 oz / 2.24 pounds), Power Supply: 222 g ( = 7.83 oz / 0.49 pounds)
Price
1349 Euro

 

Case

The Asus ZenBook S is a typical ZenBook when it comes to the design: Besides the polished edges, you also get a pattern of concentric circles on the lid. Our test model is the "Deep Dive Blue" version, which combines dark blue surfaces with golden contrast elements. The result looks very dignified, but the touchpad uses a slightly different shade of blue. This is also the case for the "Burgundy Red" model, which was shown at Computex. We added corresponding images further below. We would have preferred a more uniform color scheme, but this is certainly a matter of taste. The bezels are pleasantly slim at 5.9 mm and result in a good screen-to-body ratio of 85%, even though the XPS 13 is even better in this respect.

Typical ZenBook design elements: Polished edges and concentric circles
Typical ZenBook design elements: Polished edges and concentric circles
There are two narrow rubberized feet at the back of the hinge.
There are two narrow rubberized feet at the back of the hinge.

Both the base unit and the lid are made of a metal alloy and the manufacturer claims the manufacturing process consists of 40 steps. Asus also performed MIL-STD 810G tests like extreme temperatures, humidity etc., which is unusual for consumer devices. However, the manufacturer does not disclose the individual tests that were performed. The stability of the chassis leaves an excellent impression. Both the base unit and the lid are very sturdy considering the slim construction and there is only minor creaking when you try to twist it. Even concentrated pressure at the rear of the lid does not cause picture distortions.

The unusual hinge is obviously the design highlight. Once you open it, the base unit is lifted a bit by 5.5 degrees. There are two narrow rubberized feet at the back of the lid, so the laptop does not slide around on flat surfaces. However, the rear edge is a bit annoying when you use the device on your lap, for example. In return, the lid does not wobble even when there are vibrations. The maximum opening angle is 145 degrees, which should suffice in practice. All in all a very good performance.

At 1018 grams (~2.24 lb), the Asus ZenBook S is the lightest device in this comparison, but the height of 12.9 mm is just average since devices like the Huawei MateBook XDell XPS 13 and the HP Spectre 13 in particular are even slimmer. The ZenBook is also comparatively wide when we look at the footprint, but not very deep. Still, the subnotebook should easily fit in every bag. The wall power adapter is pretty compact and tips the scale at 222 grams (~7.8 oz).

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Size Comparison

Connectivity

The included Mini Dock is not always the best solution if you want to attach regular USB devices.
The included Mini Dock is not always the best solution if you want to attach regular USB devices.

Slimmer construction usually results in reduced port variety. The Asus ZenBook S also follows the current trend to rely on USB-C jacks with one USB-C Gen.1 port on the left and two full-fledged Thunderbolt 3 ports on the right side. All three ports support fast charge, video output, and obviously data transfers. You also get a traditional 3.5 mm stereo jack at the right back, but there is unfortunately no SD-card reader.

The box of the ZenBook S also includes the Asus Mini Dock, which provides additional ports including a regular USB Type-A port and HDMI out. There is also a USB-C port (CD-in) for power supply, which would not be important for the ZenBook S, but it makes it easy to set up the docking station on your desk. Still, compact USB-C adapters are more convenient if you just want to attach a USB device like an external hard drive.

Left side: USB Type-C 3.1 Gen.1, status LEDs
Left side: USB Type-C 3.1 Gen.1, status LEDs
Right side: 2x USB Type-C 3.1 Gen.2 (Thunderbolt 3), 3.5 mm stereo jack
Right side: 2x USB Type-C 3.1 Gen.2 (Thunderbolt 3), 3.5 mm stereo jack

Communication

Wireless communications are handled by the familiar Intel Wireless-AC 8265 module. Its successor, the Intel 9250/9260, is already starting to pop up in some devices and would provide higher transfer rates as well as Bluetooth 5.0, but the 8265 is still a solid performer. The ZenBook S does not have to hide within the comparison group, either. Besides fast ac networks, the module also supports Bluetooth 4.2. We did not notice any problems with the wireless connection during our review period.

Networking
iperf3 Client (receive) TCP 1 m 4M x10
Huawei Matebook X Pro i5
Intel Dual Band Wireless-AC 8265
660 MBit/s ∼100% +6%
Apple MacBook Pro 13 2017
802.11 a/b/g/n/ac
657 MBit/s ∼100% +5%
Asus ZenBook S UX391U
Intel Dual Band Wireless-AC 8265
625 MBit/s ∼95%
Dell XPS 13 9370 FHD i5
Atheros/Qualcomm QCA6174
588 MBit/s ∼89% -6%
Average of class Subnotebook
  (71 - 950, n=75)
535 MBit/s ∼81% -14%
HP Spectre 13-af033ng
Intel Dual Band Wireless-AC 8265
522 MBit/s ∼79% -16%
Huawei MateBook X
Intel Dual Band Wireless-AC 8265
520 MBit/s ∼79% -17%
iperf3 Client (transmit) TCP 1 m 4M x10
HP Spectre 13-af033ng
Intel Dual Band Wireless-AC 8265
659 MBit/s ∼100% +30%
Huawei MateBook X
Intel Dual Band Wireless-AC 8265
644 MBit/s ∼98% +27%
Dell XPS 13 9370 FHD i5
Atheros/Qualcomm QCA6174
557 MBit/s ∼85% +10%
Average of class Subnotebook
  (72 - 949, n=75)
521 MBit/s ∼79% +3%
Huawei Matebook X Pro i5
Intel Dual Band Wireless-AC 8265
513 MBit/s ∼78% +1%
Asus ZenBook S UX391U
Intel Dual Band Wireless-AC 8265
507 MBit/s ∼77%
Apple MacBook Pro 13 2017
802.11 a/b/g/n/ac
503 MBit/s ∼76% -1%

Accessory

Asus put some effort into the packaging and you will find some accessories in the box of the ZenBook S, which are often sold separately on competing models. You get a color-matched sleeve with a magnetic lock, which leaves a very good impression. Then there is the Asus Mini Dock we already talked about. It provides a regular USB-A port as well as HDMI out. There is also a USB-C power input, which can make sense if you plan to use the Mini Dock as a docking solution on your desk. Asus does not offer any other dedicated accessories for the ZenBook S.

Scope of delivery
Scope of delivery
Asus Mini Dock
Asus Mini Dock

Maintenance

The bottom panel of the ZenBook S UX391 is secured by multiple Torx screws and can be removed, but there is not much to do. Both the processor and the memory are soldered onto the mainboard, so you can only replace the M.2-2280 SSD. The battery is only held by screws and could be replaced if necessary.

Warranty

The warranty period is 12 months.

Input Devices - ErgoLift improves ergonomics

Keyboard

Overall, we like the keyboard of the ZenBook S and it benefits from the special hinge construction. When the lid is open, the base unit is tilted by 5.5 degrees, which improves ergonomics. The slightly concave keys provide a decent 1.2 mm travel considering the slim construction. We did not experience any issues when typing on the keyboard, which is a result of the precise stroke. The regular keys do not clatter too much, only larger keys like Return/Space bar were a bit louder on our test model.

It is easy to see the key lettering thanks to the high contrast and you also get a white background illumination (three intensity levels) for more comfortable typing in darker environments.

Input devices
Input devices
Keyboard illumination
Keyboard illumination

Touchpad

The touchpad has a smooth surface (10.5 x 6.2 cm/~4.1 x 2.4 in) and its color differs slightly from the rest of the base unit. Gliding capabilities are good and there is sufficient space for multi-touch gestures with up to four fingers. It is a Microsoft Precision touchpad and we did not experience any problems with cursor movements. Asus integrates a touch fingerprint scanner in the upper right corner, which works well and does not interfere with cursor controls.

Display

Subpixel array
Subpixel array
Backlight bleeding
Backlight bleeding

We already mentioned there are three different display options, even though both the matte FHD panel and the 4K touchscreen are only available in combination with the blue chassis option. Our test model uses the matte 1080p screen from the manufacturer AU Optronics (B133HAN04.9).

The subjective impression of the panel is decent, and even bright areas are not looking grainy despite the matte surface. However, there is a visible blue cast (more on that below) and the average luminance of 300 nits is quite low among the competition. Only the HP Spectre 13 is on a similar level, while all other models are sometimes much brighter.

We did not detect PWM, but there is some backlight bleeding at the lower edge. It is fortunately not noticeable in everyday situations.

293
cd/m²
317
cd/m²
311
cd/m²
292
cd/m²
299
cd/m²
297
cd/m²
293
cd/m²
301
cd/m²
294
cd/m²
Distribution of brightness
X-Rite i1Pro 2
Maximum: 317 cd/m² Average: 299.7 cd/m² Minimum: 16 cd/m²
Brightness Distribution: 92 %
Center on Battery: 298 cd/m²
Contrast: 1150:1 (Black: 0.26 cd/m²)
ΔE Color 5.6 | 0.4-29.43 Ø6.3, calibrated: 2.6
ΔE Greyscale 5.5 | 0.64-98 Ø6.5
90.3% sRGB (Argyll 3D) 58.9% AdobeRGB 1998 (Argyll 3D)
Gamma: 2.47
Asus ZenBook S UX391U
AUO B133HAN04.9, , 1920x1080, 13.3
Dell XPS 13 9370 FHD i5
SHP1484, , 1920x1080, 13.3
HP Spectre 13-af033ng
AU Optronics AUO422D, , 1920x1080, 13.3
Huawei Matebook X Pro i5
Tianma XM, , 3000x2000, 13.9
Huawei MateBook X
Chi Mei CMN8201 / P130ZDZ-EF1, , 2160x1440, 13.3
Apple MacBook Pro 13 2017
APPA033, , 2560x1600, 13.3
Response Times
-48%
29%
11%
22%
3%
Response Time Grey 50% / Grey 80% *
44.8 (22.8, 22)
62.4 (32.4, 30)
-39%
27 (12, 15)
40%
40.4 (19.2, 21.2)
10%
33 (15, 18)
26%
42.8 (22.4, 20.4)
4%
Response Time Black / White *
29.2 (16, 13.2)
45.6 (24.4, 21.2)
-56%
24 (14, 10)
18%
25.6 (11.6, 14)
12%
24 (12, 12)
18%
28.8 (14.8, 14)
1%
PWM Frequency
1008 (20)
Screen
20%
14%
14%
19%
37%
Brightness middle
299
428
43%
304
2%
442.7
48%
408
36%
588
97%
Brightness
300
405
35%
287
-4%
428
43%
395
32%
561
87%
Brightness Distribution
92
87
-5%
80
-13%
84
-9%
88
-4%
92
0%
Black Level *
0.26
0.26
-0%
0.21
19%
0.31
-19%
0.45
-73%
0.45
-73%
Contrast
1150
1646
43%
1448
26%
1428
24%
907
-21%
1307
14%
Colorchecker DeltaE2000 *
5.6
3.8
32%
3.66
35%
2.24
60%
1.55
72%
1.7
70%
Colorchecker DeltaE2000 max. *
9.1
7.2
21%
5.66
38%
7.19
21%
2.19
76%
3.5
62%
Colorchecker DeltaE2000 calibrated *
2.6
1.11
57%
Greyscale DeltaE2000 *
5.5
4.4
20%
3.51
36%
9.7
-76%
1.91
65%
1.9
65%
Gamma
2.47 89%
2.21 100%
2.55 86%
1.42 155%
2.34 94%
2.33 94%
CCT
7533 86%
7067 92%
6955 93%
6227 104%
6491 100%
6738 96%
Color Space (Percent of AdobeRGB 1998)
58.9
62.8
7%
59
0%
61.6
5%
61
4%
77.92
32%
Color Space (Percent of sRGB)
90.3
96.4
7%
91
1%
95
5%
96
6%
99.94
11%
Total Average (Program / Settings)
-14% / 9%
22% / 17%
13% / 14%
21% / 20%
20% / 31%

* ... smaller is better

The ZenBook S comes with the Asus Splendid software preloaded, which features basic display settings. Besides different profiles, you also get a blue light filter as well as a manual color temperature control. We tested the two profiles Standard and Vivid, but determined similar deviations. The grayscale clearly shows the blue cast and the color temperature is too cool as well.

Grayscale (Splendid profile: Standard)
Grayscale (Splendid profile: Standard)
Saturation Sweeps (Splendid profile: Standard)
Saturation Sweeps (Splendid profile: Standard)
ColorChecker (Splendid profile: Standard)
ColorChecker (Splendid profile: Standard)
Grayscale (Splendid profile: Vivid)
Grayscale (Splendid profile: Vivid)
Saturation Sweeps (Splendid profile: Vivid)
Saturation Sweeps (Splendid profile: Vivid)
ColorChecker (Splendid profile: Vivid)
ColorChecker (Splendid profile: Vivid)

Our calibration reduces the luminance slightly, but the measurements - especially the grayscale - improve dramatically. The average DeltaE 2000 deviation drops to just 0.8 and both the color temperature as well as the gamma value are close to their respective ideal values. The color performance improves as well, but there are still some outliers and blue shades in particular cannot be represented more accurately by the panel.

Grayscale (calibrated)
Grayscale (calibrated)
Saturation Sweeps (calibrated)
Saturation Sweeps (calibrated)
ColorChecker (calibrated)
ColorChecker (calibrated)

A look at the color gamut once again shows the ZenBook S and the HP Spectre 13 on par, while the competition is slightly ahead. However, the panel is not suited for (semi) professional due to the color deviations anyway, but it is sufficient for some holiday pictures.

vs. sRGB: 90.3%
vs. sRGB: 90.3%
vs. AdobeRGB: 58.9%
vs. AdobeRGB: 58.9%

The luminance is not extremely high, but you can still see the display contents very well outdoors on the ZenBook S thanks to the matte display surface. As long as you can avoid reflections from direct light sources, even bright environments are no problem. There is unfortunately no light sensor for automatic adjustments based on the environment lighting.

In the sun
In the sun
In the sun
In the sun

Display Response Times

Display response times show how fast the screen is able to change from one color to the next. Slow response times can lead to afterimages and can cause moving objects to appear blurry (ghosting). Gamers of fast-paced 3D titles should pay special attention to fast response times.
       Response Time Black to White
29.2 ms ... rise ↗ and fall ↘ combined↗ 16 ms rise
↘ 13.2 ms fall
The screen shows relatively slow response rates in our tests and may be too slow for gamers.
In comparison, all tested devices range from 0.8 (minimum) to 240 (maximum) ms. » 70 % of all devices are better.
This means that the measured response time is worse than the average of all tested devices (25.7 ms).
       Response Time 50% Grey to 80% Grey
44.8 ms ... rise ↗ and fall ↘ combined↗ 22.8 ms rise
↘ 22 ms fall
The screen shows slow response rates in our tests and will be unsatisfactory for gamers.
In comparison, all tested devices range from 0.9 (minimum) to 636 (maximum) ms. » 69 % of all devices are better.
This means that the measured response time is similar to the average of all tested devices (41.2 ms).

Screen Flickering / PWM (Pulse-Width Modulation)

To dim the screen, some notebooks will simply cycle the backlight on and off in rapid succession - a method called Pulse Width Modulation (PWM) . This cycling frequency should ideally be undetectable to the human eye. If said frequency is too low, users with sensitive eyes may experience strain or headaches or even notice the flickering altogether.
Screen flickering / PWM not detected

In comparison: 53 % of all tested devices do not use PWM to dim the display. If PWM was detected, an average of 8898 (minimum: 43 - maximum: 142900) Hz was measured.

Asus implements an IPS panel so there are no issues with the viewing angles. The contents get brighter especially from angles from above or below, but this is not uncommon. The content is still perfectly visible.

Viewing angle stability
Viewing angle stability

Performance

Independent of the Windows power settings, the ZenBook S also offers a so-called Quiet Mode. You can easily activate/deactivate it via the task bar symbol and it is supposed to ensure lower temperatures as well as a quieter fan. We can confirm this statement, but it also results in a significant performance drop by limiting the TDP. The CPU can consume up to 25 watts in the normal mode (even though this cannot be maintained for long), but the Quiet Mode limits the TDP to just 5.5 watts, roughly a third of the nominal 15 watts.

We performed the benchmarks with Quiet Mode deactivated, but we will look at the impact in some of the scenarios below.

 

Processor

The ZenBook S UX391 is either equipped with the Intel Core i5-8250U or Core i7-8550U. The latter is also powering our test model and features four cores, which can execute up to eight threads simultaneously thanks to Hyperthreading. This means the multi-core performance is twice as high compared to the old dual-core ULVs, at least in theory. The actual performance depends on the cooling performance though since the quad-core ULVs consume a lot of power at high clocks and produce a lot of heat.

We determine a decent score of 602 points during the first Cinebench R15 Multi run. The Spectre 13 performs worse with the same processor, while the XPS 13 with the supposedly slower Core i5-8250U is 11% faster. The performance drops dramatically when we activate the Quiet Mode and even falls behind the old Intel Core i5-7200U.

Cinebench R15
CPU Single 64Bit
Asus ZenBook S UX391U
Intel Core i7-8550U (Quiet Mode off)
165 Points ∼100%
Asus ZenBook S UX391U
Intel Core i7-8550U (Quiet Mode on)
108 Points ∼65% -35%
Average Intel Core i7-8550U
  (108 - 172, n=55)
160 Points ∼97% -3%
Huawei Matebook X Pro i5
Intel Core i5-8250U
146 Points ∼88% -12%
Apple MacBook Pro 13 2017
Intel Core i5-7360U (macOS)
145 Points ∼88% -12%
Apple MacBook Pro 13 2017
Intel Core i5-7360U (Win10)
140 Points ∼85% -15%
HP Spectre 13-af033ng
Intel Core i7-8550U
145 Points ∼88% -12%
Dell XPS 13 9370 FHD i5
Intel Core i5-8250U
144 Points ∼87% -13%
Huawei MateBook X
Intel Core i5-7200U
116 Points ∼70% -30%
Average of class Subnotebook
  (20 - 169, n=224)
110 Points ∼67% -33%
CPU Multi 64Bit
Dell XPS 13 9370 FHD i5
Intel Core i5-8250U
669 Points ∼100% +11%
Asus ZenBook S UX391U
Intel Core i7-8550U (Quiet Mode off)
602 Points ∼90%
Asus ZenBook S UX391U
Intel Core i7-8550U (Quiet Mode on)
301 Points ∼45% -50%
Average Intel Core i7-8550U
  (301 - 761, n=57)
570 Points ∼85% -5%
Huawei Matebook X Pro i5
Intel Core i5-8250U
516 Points ∼77% -14%
HP Spectre 13-af033ng
Intel Core i7-8550U
515 Points ∼77% -14%
Apple MacBook Pro 13 2017
Intel Core i5-7360U (macOS)
362 Points ∼54% -40%
Apple MacBook Pro 13 2017
Intel Core i5-7360U (Win10)
346 Points ∼52% -43%
Huawei MateBook X
Intel Core i5-7200U
322 Points ∼48% -47%
Average of class Subnotebook
  (32 - 721, n=231)
300 Points ∼45% -50%

This level of performance cannot be maintained for very long. We see a performance drop after a few runs and the score levels off at around 380 points. The average power consumption of the CPU after 25 Cinebench Multi runs is just 10.8 W at 1.88 GHz. This will drop to just 1.25 GHz with the activated Quiet Mode.

This is not a very good performance, even when you consider the slim construction. The slimmer Dell XPS 13 is much faster under load (~600 points).

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Cinebench R15 CPU Multi 64 Bit Rot: Quiet Mode off, Gelb: Quiet Mode on
Cinebench R15 CPU Single 64Bit
108 Points
Cinebench R15 CPU Multi 64Bit
301 Points
Cinebench R15 OpenGL 64Bit
53.8 fps
Cinebench R15 Ref. Match 64Bit
97.8 %
Help

System Performance

You get all the ingredients for a responsive system: quad-core ULV processor, sufficient RAM, and especially the fast PCIe-SSD. We are not disappointed by the ZenBook, because our inputs are quickly executed and applications are launched without any noticeable delays. The PCMark scores differ depending on the sub test. While the ZenBook S can secure a great second spot in the PCMark 8 Work test, it drops to the end of the comparison in the Home test as well as the current PCMark 10. Still, all the comparison devices perform on a good level and there should not be any problems with the ZenBook S in practice.

PCMark 8
Work Score Accelerated v2
Dell XPS 13 9370 FHD i5
UHD Graphics 620, 8250U, Toshiba XG5 KXG50ZNV256G
4906 Points ∼100% 0%
Asus ZenBook S UX391U
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
4882 Points ∼100%
HP Spectre 13-af033ng
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
4562 Points ∼93% -7%
Average Intel Core i7-8550U, Intel UHD Graphics 620
  (3518 - 5154, n=17)
4545 Points ∼93% -7%
Apple MacBook Pro 13 2017
Iris Plus Graphics 640, 7360U, Apple SSD AP0128
4461 (min: 4448, max: 4484) Points ∼91% -9%
Huawei Matebook X Pro i5
GeForce MX150, 8250U, Samsung PM961 MZVLW256HEHP
4339 Points ∼88% -11%
Huawei MateBook X
HD Graphics 620, 7200U, LITEON CB1-SD256
4276 Points ∼87% -12%
Average of class Subnotebook
  (1283 - 5363, n=170)
3926 Points ∼80% -20%
Creative Score Accelerated v2
Apple MacBook Pro 13 2017
Iris Plus Graphics 640, 7360U, Apple SSD AP0128
5544 (min: 5539, max: 5549) Points ∼100% +18%
Dell XPS 13 9370 FHD i5
UHD Graphics 620, 8250U, Toshiba XG5 KXG50ZNV256G
5044 Points ∼91% +7%
HP Spectre 13-af033ng
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
5011 Points ∼90% +6%
Huawei Matebook X Pro i5
GeForce MX150, 8250U, Samsung PM961 MZVLW256HEHP
4747 Points ∼86% +1%
Asus ZenBook S UX391U
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
4707 Points ∼85%
Average Intel Core i7-8550U, Intel UHD Graphics 620
  (3381 - 5342, n=15)
4691 Points ∼85% 0%
Average of class Subnotebook
  (1011 - 5544, n=135)
3543 Points ∼64% -25%
Home Score Accelerated v2
Apple MacBook Pro 13 2017
Iris Plus Graphics 640, 7360U, Apple SSD AP0128
4057 (min: 4055, max: 4059) Points ∼100% +14%
Dell XPS 13 9370 FHD i5
UHD Graphics 620, 8250U, Toshiba XG5 KXG50ZNV256G
3994 Points ∼98% +12%
HP Spectre 13-af033ng
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
3705 Points ∼91% +4%
Average Intel Core i7-8550U, Intel UHD Graphics 620
  (3255 - 4017, n=19)
3632 Points ∼90% +2%
Asus ZenBook S UX391U
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
3554 Points ∼88%
Huawei MateBook X
HD Graphics 620, 7200U, LITEON CB1-SD256
3507 Points ∼86% -1%
Huawei Matebook X Pro i5
GeForce MX150, 8250U, Samsung PM961 MZVLW256HEHP
3478 Points ∼86% -2%
Average of class Subnotebook
  (1027 - 4182, n=194)
2978 Points ∼73% -16%
PCMark 10 - Score
Apple MacBook Pro 13 2017
Iris Plus Graphics 640, 7360U, Apple SSD AP0128
3840 (min: 3824, max: 3845) Points ∼100% +16%
Dell XPS 13 9370 FHD i5
UHD Graphics 620, 8250U, Toshiba XG5 KXG50ZNV256G
3764 Points ∼98% +13%
Average Intel Core i7-8550U, Intel UHD Graphics 620
  (2629 - 4012, n=16)
3500 Points ∼91% +5%
Huawei Matebook X Pro i5
GeForce MX150, 8250U, Samsung PM961 MZVLW256HEHP
3445 Points ∼90% +4%
Asus ZenBook S UX391U
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
3321 Points ∼86%
Average of class Subnotebook
  (1150 - 3860, n=43)
2911 Points ∼76% -12%
PCMark 8 Home Score Accelerated v2
3554 points
PCMark 8 Creative Score Accelerated v2
4707 points
PCMark 8 Work Score Accelerated v2
4882 points
Help

Storage Devices

The ZenBook S UX391 is only shipped with M.2-SSDs, but the interface can differ. The smaller 256 GB model is attached via SATA-3, while the faster NVMe protocol (PCIe x4) is reserved for the bigger versions with 512 GB or 1 TB storage, respectively. The 512 GB SSD in our test model is provided by Samsung and carries the designation PM961, so it is one of the fastest drives on the market. Our benchmarks confirm the high performance with sequential read speeds of more than 3200 MB/s and 1600 MB/s sequential write, respectively. The 4K performance, which is important when you launch applications or boot the device, is also good. However, Asus might use several suppliers and you might not always get the Samsung SSD.

See our comprehensive HDD/SSD list for more benchmarks and comparison.

Samsung PM961 NVMe MZVLW512HMJP
Sequential Read: 1804.5 MB/s
Sequential Write: 1437.9 MB/s
512K Read: 653.83 MB/s
512K Write: 1106.7 MB/s
4K Read: 47.75 MB/s
4K Write: 101.04 MB/s
4K QD32 Read: 257.2 MB/s
4K QD32 Write: 364.63 MB/s

GPU Performance

All the graphics calculations are handled by the integrated GPU of the processor, the UHD Graphics 620. It offers sufficient performance for multimedia applications including streaming and playback of high-resolution videos. However, the ZenBook is a bit slower than the rivals. It should benefit from the dual-channel memory configuration, but it is still at the bottom of the comparison group most of the time. This is probably connected to the cooling performance, so the iGPU cannot utilize its full potential.

More technical information and benchmarks for the Intel UHD Graphics 620 are available here.

3DMark 11 - 1280x720 Performance GPU
Huawei Matebook X Pro i5
NVIDIA GeForce MX150, Intel Core i5-8250U
3483 Points ∼100% +142%
Apple MacBook Pro 13 2017
Intel Iris Plus Graphics 640, Intel Core i5-7360U
2379 (min: 2355, max: 2425) Points ∼68% +65%
Dell XPS 13 9370 FHD i5
Intel UHD Graphics 620, Intel Core i5-8250U
1776 Points ∼51% +23%
Average Intel UHD Graphics 620
  (1235 - 1915, n=86)
1657 Points ∼48% +15%
HP Spectre 13-af033ng
Intel UHD Graphics 620, Intel Core i7-8550U
1587 Points ∼46% +10%
Huawei MateBook X
Intel HD Graphics 620, Intel Core i5-7200U
1528 Points ∼44% +6%
Asus ZenBook S UX391U
Intel UHD Graphics 620, Intel Core i7-8550U
1440 Points ∼41%
Average of class Subnotebook
  (230 - 4191, n=313)
1137 Points ∼33% -21%
3DMark
1920x1080 Fire Strike Graphics
Huawei Matebook X Pro i5
NVIDIA GeForce MX150, Intel Core i5-8250U
2740 Points ∼100% +175%
Apple MacBook Pro 13 2017
Intel Iris Plus Graphics 640, Intel Core i5-7360U
1541 (min: 1484, max: 1547) Points ∼56% +55%
Dell XPS 13 9370 FHD i5
Intel UHD Graphics 620, Intel Core i5-8250U
1100 Points ∼40% +10%
Average Intel UHD Graphics 620
  (557 - 1336, n=75)
1069 Points ∼39% +7%
HP Spectre 13-af033ng
Intel UHD Graphics 620, Intel Core i7-8550U
1052 Points ∼38% +6%
Asus ZenBook S UX391U
Intel UHD Graphics 620, Intel Core i7-8550U
997 Points ∼36%
Average of class Subnotebook
  (222 - 3389, n=201)
911 Points ∼33% -9%
Huawei MateBook X
Intel HD Graphics 620, Intel Core i5-7200U
875 Points ∼32% -12%
1280x720 Cloud Gate Standard Graphics
Huawei Matebook X Pro i5
NVIDIA GeForce MX150, Intel Core i5-8250U
16553 Points ∼100% +125%
Apple MacBook Pro 13 2017
Intel Iris Plus Graphics 640, Intel Core i5-7360U
11495 (min: 10969, max: 11750) Points ∼69% +56%
HP Spectre 13-af033ng
Intel UHD Graphics 620, Intel Core i7-8550U
8787 Points ∼53% +19%
Average Intel UHD Graphics 620
  (6910 - 10493, n=79)
8733 Points ∼53% +18%
Huawei MateBook X
Intel HD Graphics 620, Intel Core i5-7200U
7542 Points ∼46% +2%
Asus ZenBook S UX391U
Intel UHD Graphics 620, Intel Core i7-8550U
7372 Points ∼45%
Average of class Subnotebook
  (1484 - 18946, n=223)
6801 Points ∼41% -8%
3DMark 11 Performance
1592 points
3DMark Ice Storm Standard Score
39992 points
3DMark Cloud Gate Standard Score
6256 points
3DMark Fire Strike Score
897 points
Help

Gaming Performance

The GPU benchmarks already indicated that the ZenBook S is not a great choice for gaming. Even older titles like Bioshock Infinite or Tomb Raider from 2013 only run smoothly at the lowest settings. Similar to the CPU performance, the Quiet Mode has a massive impact on the gaming performance. The frame rate in Bioshock Infinite (Low), for instance, drops from 52.8 to just 26.1 fps.

low med. high ultra
Tomb Raider (2013) 78.139.227.412.4fps
BioShock Infinite (2013) 52.830.726.79fps
The Witcher 3 (2015) 17.3fps

Emissions

System Noise – Quiet Mode works

Fan of the ZenBook S UX391
Fan of the ZenBook S UX391

There is not much room for a fan inside a slim chassis, so most ultra-slim laptops can have a pretty loud and high-pitched fan noise. Asus implements a feature called Quiet Mode, which gives the user a direct method to change the fan noise.

The fan is usually deactivated while running, but it reacts quickly to load scenarios. The fan noise itself is fortunately not annoying. We measure up to 36.8 dB(A) during the stress test, but this value drops over time due to the throttling behavior (36.8 -> 35.3 -> 33.1 -> 31.9 dB(A)). The activated Quiet Mode limits the fan noise to a maximum value of 30.5 dB(A), so the fan is basically inaudible even under load.

We noticed occasional electronic noises, but were not able to determine the cause.

Noise Level

Idle
29.7 / 29.7 / 30.1 dB(A)
Load
36.8 / 36.8 dB(A)
  red to green bar
 
 
30 dB
silent
40 dB(A)
audible
50 dB(A)
loud
 
min: dark, med: mid, max: light   Audix TM1, Arta (15 cm distance)   environment noise: 29.7 dB(A)
Asus ZenBook S UX391U
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
Dell XPS 13 9370 FHD i5
UHD Graphics 620, 8250U, Toshiba XG5 KXG50ZNV256G
HP Spectre 13-af033ng
UHD Graphics 620, 8550U, Samsung PM961 NVMe MZVLW512HMJP
Huawei Matebook X Pro i5
GeForce MX150, 8250U, Samsung PM961 MZVLW256HEHP
Apple MacBook Pro 13 2017
Iris Plus Graphics 640, 7360U, Apple SSD AP0128
Noise
3%
3%
1%
-0%
off / environment *
29.7
29.1
2%
30.13
-1%
27.9
6%
30.2
-2%
Idle Minimum *
29.7
29.1
2%
30.13
-1%
27.9
6%
30.2
-2%
Idle Average *
29.7
29.1
2%
30.13
-1%
27.9
6%
30.2
-2%
Idle Maximum *
30.1
29.1
3%
30.13
-0%
27.9
7%
30.2
-0%
Load Average *
36.8
32.2
12%
31.5
14%
36.2
2%
32.9
11%
Load Maximum *
36.8
37.3
-1%
33.5
9%
45.2
-23%
39.3
-7%
Witcher 3 ultra *
45

* ... smaller is better

Temperature

The temperature development is obviously a challenge for a slim device. We have already seen reduced performance figures under sustained workloads above, which have an effect on the temperatures as well. There is no noteworthy warming up while idling and under light workloads, and the hot spots under load are concentrated on the rear center area, where the processor and the cooling unit are located.

A look at the CPU performance during the stress test shows the level of throttling. The CPU consumption (including the integrated graphics adapter) already drops below 10 watts after about 2 minutes, so it is well below the nominal 15 watts classification.

Max. Load
 35.6 °C
96 F
40.3 °C
105 F
36 °C
97 F
 
 30.5 °C
87 F
33.2 °C
92 F
32.6 °C
91 F
 
 25.7 °C
78 F
25.5 °C
78 F
26.9 °C
80 F
 
Maximum: 40.3 °C = 105 F
Average: 31.8 °C = 89 F
37.1 °C
99 F
41.5 °C
107 F
38.1 °C
101 F
33.4 °C
92 F
34 °C
93 F
30.9 °C
88 F
27 °C
81 F
27.5 °C
82 F
26.8 °C
80 F
Maximum: 41.5 °C = 107 F
Average: 32.9 °C = 91 F
Power Supply (max.)  28.8 °C = 84 F | Room Temperature 21.6 °C = 71 F | Voltcraft IR-900
Temperature development stress test
Temperature development stress test

Speakers

One of the speaker modules
One of the speaker modules

The sound performance on slim devices is a challenge and our expectations are usually not very high. The two speakers at the bottom front of the ZenBook S UX391 are not overly loud, but the subjective impression is decent. Their performance is definitely sufficient for some music and video playback/streaming, even though there is no bass due to the construction. The stereo jack also provides a noise-free signal when you want to attach headphones or external speakers.

dB(A) 0102030405060708090Deep BassMiddle BassHigh BassLower RangeMidsHigher MidsLower HighsMid HighsUpper HighsSuper Highs2033.532.32531.930.93131.639.24029.336.45030.835.16326.2318025.831.110027.330.812523.640.816023.350.520021.856.425021.356.431520.35540019.456.150018.957.963018.45980017.557.3100017.461.8125017.169.8160016.867.6200016.671.1250016.770.7315016.965.8400017.467.5500017.668.8630017.865.5800017.865.31000017.968.61250017.869.71600017.767.8SPL29.779.7N1.344.3median 17.8Asus ZenBook S UX391Umedian 65.3Delta1.66.534.230.529.729.430.228.43028.227.529.126.82824.925.723.832.12335.121.948.621.752.62157.419.558.119.158.718.262.718.26517.371.917.371.816.772.11672.615.672.715.968.616.168.916.465.916.571.616.973.717.172.617.167.217.163.71755.329.182.81.255.8median 17.1Dell XPS 13 9370 FHD i5median 65.91.58.6hearing rangehide median Pink Noise
Frequency diagram (checkboxes can be checked and unchecked to compare devices)
Asus ZenBook S UX391U audio analysis

(±) | speaker loudness is average but good (79.7 dB)
Bass 100 - 315 Hz
(-) | nearly no bass - on average 17% lower than median
(±) | linearity of bass is average (9.6% delta to prev. frequency)
Mids 400 - 2000 Hz
(±) | reduced mids - on average 5.9% lower than median
(+) | mids are linear (6.3% delta to prev. frequency)
Highs 2 - 16 kHz
(+) | balanced highs - only 2.1% away from median
(+) | highs are linear (4.5% delta to prev. frequency)
Overall 100 - 16.000 Hz
(±) | linearity of overall sound is average (15.6% difference to median)
Compared to same class
» 30% of all tested devices in this class were better, 13% similar, 57% worse
» The best had a delta of 8%, average was 19%, worst was 47%
Compared to all devices tested
» 19% of all tested devices were better, 4% similar, 78% worse
» The best had a delta of 3%, average was 21%, worst was 53%

Dell XPS 13 9370 FHD i5 audio analysis

(+) | speakers can play relatively loud (82.8 dB)
Bass 100 - 315 Hz
(-) | nearly no bass - on average 18.6% lower than median
(±) | linearity of bass is average (11.1% delta to prev. frequency)
Mids 400 - 2000 Hz
(±) | higher mids - on average 5.3% higher than median
(+) | mids are linear (3.8% delta to prev. frequency)
Highs 2 - 16 kHz
(+) | balanced highs - only 3.9% away from median
(+) | highs are linear (6.4% delta to prev. frequency)
Overall 100 - 16.000 Hz
(±) | linearity of overall sound is average (17.3% difference to median)
Compared to same class
» 47% of all tested devices in this class were better, 6% similar, 47% worse
» The best had a delta of 8%, average was 19%, worst was 47%
Compared to all devices tested
» 27% of all tested devices were better, 6% similar, 67% worse
» The best had a delta of 3%, average was 21%, worst was 53%

Energy Management

Power Consumption

Our power consumption measurements of the Asus ZenBook S UX391U do not reveal any surprises. The maximum idle consumption also accounts for the bright keyboard illumination, which increases the consumption by 2.5 watts. If you need long battery runtimes in dark environments, you should only use the darkest illumination level. The maximum consumption is 52.6 watts, but this value drops to just 22 watts after the stress test due to the throttling. The provided 65W power adapter is more than sufficient.

Power Consumption
Off / Standbydarklight 0.48 / 0.73 Watt
Idledarkmidlight 3.24 / 6.1 / 9.2 Watt
Load midlight 38.8 / 52.6 Watt
 color bar
Key: min: dark, med: mid, max: light        Metrahit Energy
Asus ZenBook S UX391U
8550U, UHD Graphics 620, Samsung PM961 NVMe MZVLW512HMJP, IPS, 1920x1080, 13.3
Dell XPS 13 9370 FHD i5
8250U, UHD Graphics 620, Toshiba XG5 KXG50ZNV256G, IPS, 1920x1080, 13.3
HP Spectre 13-af033ng
8550U, UHD Graphics 620, Samsung PM961 NVMe MZVLW512HMJP, IPS, 1920x1080, 13.3
Huawei Matebook X Pro i5
8250U, GeForce MX150, Samsung PM961 MZVLW256HEHP, IPS, 3000x2000, 13.9
Huawei MateBook X
7200U, HD Graphics 620, LITEON CB1-SD256, , 2160x1440, 13.3
Apple MacBook Pro 13 2017
7360U, Iris Plus Graphics 640, Apple SSD AP0128, IPS, 2560x1600, 13.3
Average Intel UHD Graphics 620
 
Average of class Subnotebook
 
Power Consumption
11%
11%
-25%
-24%
3%
0%
-35%
Idle Minimum *
3.24
3.14
3%
2.8
14%
3.5
-8%
4.6
-42%
3.7
-14%
3.84 (2 - 8.5, n=87)
-19%
6.88 (1 - 36, n=549)
-112%
Idle Average *
6.1
5.22
14%
6.2
-2%
8.9
-46%
11
-80%
5.2
15%
7 (4.3 - 11.8, n=87)
-15%
10.1 (2.06 - 39, n=549)
-66%
Idle Maximum *
9.2
6
35%
9.4
-2%
12.3
-34%
12
-30%
7.6
17%
8.64 (5.2 - 13.1, n=87)
6%
12.4 (3.9 - 55, n=549)
-35%
Load Average *
38.8
38.5
1%
32.2
17%
54.2
-40%
39.5
-2%
41.6
-7%
35.4 (15 - 51.1, n=87)
9%
33.2 (6.3 - 75, n=539)
14%
Load Maximum *
52.6
50.4
4%
36.6
30%
52.1
1%
34.6
34%
50.5
4%
41.5 (22 - 71.2, n=87)
21%
40.2 (7.6 - 111, n=542)
24%
Witcher 3 ultra *
42.4

* ... smaller is better

Battery Runtime

Charging
Charging

The 50 Wh battery of the Asus ZenBook S UX391 provides decent battery runtimes, but some of the rivals last much longer. Our WLAN test at an adjusted luminance of 150 nits only determines little more than 8 hours. Not a bad result in general, but the competition from Dell, Huawei, and Apple are superior in this scenario.

The situation is better in the video playback test (again at 150 nits) and the 10.5 hours of the ZenBook S are close to the Apple MacBook Pro. Only the XPS 13 from Dell has much more stamina and last almost 14 hours. Our load test runs for about 2 hours.

Asus advertises a quick-charge functionality for 60% of the capacity after 49 minutes. We can confirm this by our tests. Starting at 5% remaining (Windows standard value for critical battery capacity) it takes about 48 minutes for ~60% capacity. The remaining 35% take - as per usual - longer, which results in a total charging time of little more than two hours.

Battery Runtime
Idle (without WLAN, min brightness)
22h 20min
NBC WiFi Websurfing Battery Test 1.3 (Edge 42.17134.1.0)
8h 11min
Big Buck Bunny H.264 1080p
10h 21min
Load (maximum brightness)
1h 55min
Asus ZenBook S UX391U
8550U, UHD Graphics 620, 50 Wh
Dell XPS 13 9370 FHD i5
8250U, UHD Graphics 620, 52 Wh
HP Spectre 13-af033ng
8550U, UHD Graphics 620, 43 Wh
Huawei Matebook X Pro i5
8250U, GeForce MX150, 57.4 Wh
Huawei MateBook X
7200U, HD Graphics 620, 40 Wh
Apple MacBook Pro 13 2017
7360U, Iris Plus Graphics 640, 54.5 Wh
Average of class Subnotebook
 
Battery Runtime
23%
-11%
15%
5%
6%
-10%
H.264
621
831
34%
649
5%
683
10%
453 (182 - 950, n=97)
-27%
WiFi v1.3
491
644
31%
352
-28%
557
13%
337
-31%
681
39%
457 (206 - 805, n=165)
-7%
Load
115
119
3%
104
-10%
133
16%
162
41%
78
-32%
121 (40 - 327, n=528)
5%

Verdict

Pros

+ high-quality metal case; light and slim
+ matte FHD screen
+ quiet operation, optional Quiet Mode
+ 2x Thunderbolt 3
+ docking station & sleeve included
+ decent input devices

Cons

- mediocre performance utilization
- fan quickly spins up under load
- battery runtime could be longer
- no SD reader
- occasional electronic noises
In review: Asus ZenBook S (UX391). Test model courtesy of Asus Germany.
In review: Asus ZenBook S (UX391). Test model courtesy of Asus Germany.

How much performance does a mobile device need? Slim devices often have issues to utilize the performance potential of the current mobile quad-core processors. However, everyday tasks usually do not need that level of performance. We like the approach with an additional Quiet Mode, which is more comprehensive compared to the regular Windows power settings or Performance Slider, respectively.

Asus' new ZenBook S UX391 is extremely mobile and targets customers that are often on the road and require a compact device. Very complex applications are usually not on top of the list of requirements, and most of the time it will be used to write mails, use cloud based apps or just use the Office suite. The performance of the ZenBook S is more than sufficient for these scenarios, even when you activate the Quiet Mode.

The ZenBook S UX391 is a very good choice if you want a very light and compact companion. However, some of the rivals can utilize the performance of the ULV quad-core better and last longer on battery. 

You also get a high-quality device with a metal chassis and good build quality. We like the matte 1080p screen, even though it could be a bit brighter and better calibrated ex-works. The input devices are decent and Asus implements modern ports. A small docking station adds traditional ports and is included.

We already mentioned the mediocre performance above. If you need more performance in a compact chassis, you should look out for another model. Otherwise, we can recommend the ZenBook S UX391.

Asus ZenBook S UX391U - 09/11/2018 v6
Andreas Osthoff

Chassis
89 /  98 → 91%
Keyboard
83%
Pointing Device
90%
Connectivity
61 / 80 → 77%
Weight
75 / 35-78 → 93%
Battery
91%
Display
86%
Games Performance
57 / 68 → 84%
Application Performance
79 / 87 → 90%
Temperature
93 / 91 → 100%
Noise
95%
Audio
68 / 91 → 75%
Camera
42 / 85 → 49%
Average
78%
89%
Subnotebook - Weighted Average

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> Notebook / Laptop Reviews and News > Reviews > Asus ZenBook S UX391U (Core i7, FHD) Laptop Review
Andreas Osthoff, 2018-09-14 (Update: 2018-09-15)
Andreas Osthoff
Andreas Osthoff - Senior Editor Business
I grew up with computers and modern consumer electronics. I am interested in the technology since I had my first computer, a Commodore C64, and started building my own PCs after that. My focus here at Notebookcheck is the business segment including mobile workstations, but I also like to test new mobile devices. It is always a great experience to review and compare new products. My free time is filled with a lot of sports, in the summer mainly on my bike.