Lian Li B4-mATX Review: a compact mATX SFF case with excellent airflow and premium features

TweakTown Rating: 99%

Our Verdict

The Lian Li B4-mATX is an affordable $69.99 SFF chassis delivering exceptional airflow, premium hardware support, and superb thermal performance. Despite minor clearance limitations for thick coolers and power supplies, its modular design makes it a top-tier choice for compact builds.

Pros

• Very aggressive pricing
• Includes 2 120mm, 15mm thick fans pre-installed
• Can be used horizontally or vertically with the AeroDeck panel
• Supports large GPUs like the ASUS ROG RTX 5080 Astrel

Cons

• In order to use a 360mm AIO, an SFX PSU must be used
• Only thin AIOs need to apply

Should you buy it?

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Introduction, Specifications, and Pricing

Lian Li and Dan have been collaborating for a while, and today we see their newest creation: the B4-mATX. Lian Li and Dan are launching a new mATX SFF case in 2026, and that motherboard format is becoming more popular lately. The B4-mATX is made for the SFF enthusiast who wants high-end hardware, with support for up to a 360mm radiator for CPU cooling. Lian Li has set the MSRP at $69.99 for the base mesh model, with only a $5 upcharge for the white color option. Two additional models include wood accents on the front panel for $84.99 (black) and $89.99 (white). The B4 mATX can also be configured with an optional vertical AeroDeck front panel that flips the orientation for a more tower-like appearance, for an additional $29.99.

So, why don't we see how this 21.3-liter SFF case handles some high-end hardware alongside a 360mm AIO? Let's build.

Packaging

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Packaged in a simple brown cardboard box, Lian Li and Dan place the B4-mATX in the center with the phrase "Build like never B4." I see what you did there, Lian Li.

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After opening and removing the B4-mATX from its cardboard exterior, Lian Li places it between two closed-cell foam end pieces and inside a clear bag to keep debris out.

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Outside the Lian Li B4 mATX Chassis

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The front mesh pane slides up for removal and is fully meshed with no branding.

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Another view of the front mesh panel shows clean, unobstructed airflow.

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The right-side panel, removed after the front panel by sliding it to the rear, is similarly clean and unobstructed, a common theme.

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The rear of the B4-mATX follows the traditional mATX layout, with an invertible 120mm motherboard fan location at the rear if the end user chooses an AeraDeck layout. The C13 power cable input is located on the top with a swing-out design.

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The left side panel, identical to the right, features a fully meshed side.

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The top panel lifts out via the tab and is fully meshed, with the front I/O at the top.

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Moving to the underside, we have a full-length dust filter and four removable rubber feet.

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Before we go inside the B4-mATX, let's have a look at the front/top I/O: two USB 3.0 Type-A ports, a round power button, a combo 3.5 mm mic/headset jack, and a USB Type-C port.

Inside the Lian Li B4 mATX Chassis

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Removing the top panel via the tab gives us access to the two included Lian Li 120mm, 15mm thick fans. Rated for 64.2 CFM each at 1800RPM +/- 10%, these fans exhaust a good amount of hot air.

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With all the panels off, the B4-mATX is fully exposed. The front panel accommodates a 120mm fan in front of the GPU, providing fresh intake air. Above that fan mount is a 2.5in HDD or SSD mount, with another 2.5in HDD or SSD mount on the inside floor.

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Going around to the other side, we find a large motherboard cutout along with PSU mounting options.

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Of course, there is a special badge showing the collaboration between Dan Case and Lian Li.

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In the main compartment, we first find a bracket that accepts up to a 360mm AIO, albeit a thin 25mm model due to space restrictions, but a 360mm AIO nonetheless.

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All the cabling is bundled to the PSU cage, which can be removed to accept an SFX PSU and enable other hardware configurations.

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And finally, we have a simple thank-you card inside the "tackle box" of various screws and other accessories.

Installation, Testing, Finished Product, and Final Thoughts

Ryan's Test System Specifications

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Using the mITX/mATX Case Test Hardware, which consists of an AMD Ryzen 9 7900 12-core, 24-threaded AM5 CPU on a GIGABYTE AORUS B650i Ultra motherboard, cooled by an AMD Wraith Prism CPU cooler, we saw CPU temperatures average just 62.1 °C, with a maximum of 67.5 °C. For a Ryzen 9 7900, that is absolutely amazing, especially since AM5 CPUs are meant to run near their thermal threshold while continuing the highest possible CPU clock, which is at least 4.9GHz. On the Zotac Trinity RTX 3090, the maximum temperature recorded was 82 °C, with an average of 79.7 °C, indicating that the GPU benefited from this airflow setup, particularly with the two roof exhaust fans included with the B4-mATX.

All testing was completed using Aida64 Engineer's System Stability Test version 8.00.8000 for over 7 hours, with the ambient temperature at 18 °C. Other monitoring software used was HWiNFO64 v8.30.5800, TechPowerUp GPU-Z v2.69.0, and CPU-Z 2.16.0.x64.

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Final Thoughts

The collaboration between Lian Li and Dan Case continues to yield superb results, and the B4 mATX is no exception. Entering a market where the mATX motherboard format is seeing a massive resurgence, this 21.3-liter SFF chassis strikes a phenomenal balance between compact engineering and high-end hardware support.

Moving on to the thermal performance, which is a major highlight of the B4 mATX. Thanks to its heavily meshed exterior panels and the inclusion of two pre-installed 120mm slim exhaust fans, our AMD Ryzen 9 7900 test system ran incredibly cool, averaging just 62.1°C under a grueling 7-hour stress test. Quick note: even though we did not test a 360mm AIO, mainly due to time constraints, the AMD Wraith Prism CPU cooler performed excellently. The power-hungry Zotac Trinity RTX 3090 remained well within its operating limits, proving that this case can handle top-tier components without choking airflow.

There are, of course, a few spatial trade-offs inherent to the SFF form factor. If you plan to mount a massive 360mm AIO radiator, you will need to commit to an SFX power supply and ensure your liquid cooler has a thin 25mm profile. Even so, the chassis's versatility - including the optional AeroDeck front panel for vertical tower orientation and clearance for massive GPUs like the ASUS ROG RTX 5080 Astrel - makes these limitations easy to overlook.

Starting at an incredibly aggressive MSRP of $69.99 for the base black mesh model, Lian Li and Dan have changed the small-form-factor market without sacrificing premium features, modularity, or aesthetics. Whether you stick with the budget-friendly base mesh, opt for the elegant wood-accented variants, or flip it vertically, the B4 mATX is a triumph in budget-friendly SFF design. If you are looking to downsize your setup without downsizing your performance, the B4 mATX earns a place at the very top of your shortlist.