Lian Li B4 mATX Mesh Case Black

The Lian Li B4-mATX is a compact 21.3L Micro-ATX PC case developed in collaboration with DAN Cases, combining a space efficient design with versatile hardware compatibility and flexible installation options. Measuring 420 x 191 x 288mm, it supports Micro-ATX and Mini-ITX motherboards, graphics cards up to 358mm long and four expansion slots thick, and both ATX power supplies up to 140mm long and SFX power supplies. Its adaptable layout supports horizontal desktop or vertical tower positioning, allowing users to optimise their desk space. Two pre-installed 120 x 120 x 15mm slim fans provide exhaust airflow, with additional mounting positions supporting up to nine fans depending on the configuration. Cooling options include side mounted radiators up to 360mm with an SFX power supply or 240mm with an ATX power supply, while CPU air coolers up to 165mm high are supported when the side fan bracket is removed. A reversible rear fan bracket accommodates different cooling configurations, and the removable front bracket simplifies the installation of large graphics cards. A dedicated GPU anti-sag bracket provides additional support for heavier graphics cards, while tool-less removable panels, cable routing provisions and a removable bottom dust filter help simplify assembly and maintenance. Storage support includes one front-mounted 2.5 inch SSD and space for either one additional 2.5 inch SSD or one 3.5 inch HDD at the bottom. Front I/O connectivity includes two USB Type-A ports, one USB Type-C port supporting transfer speeds up to 20Gbps, an audio connection and a power button. With its compact footprint, flexible cooling options and dual orientation design, the Lian Li B4-mATX is a versatile foundation for space-conscious gaming systems and performance-focused compact PC builds.

Features

---

B4-mATX

• Compact 21.3L mATX case with broad compatibility.
• Supports M-ATX / Mini-ITX, 358mm 4-slot GPUs, and 140mm ATX PSUs.
• Supports up to 360mm radiators with SFX PSU, or 240mm with ATX PSU.
• Up to 165mm CPU cooler clearance, or 159mm with side fan bracket.
• Includes 2 pre-installed 120 x 120 x 15mm slim top fans.
• Supports up to 9 fans across top, side, bottom, rear, and front.
• Removable top bracket simplifies CPU 8-pin routing and fan setup.
• Removable front bracket allows easier large GPU installation.
• Supports both horizontal and vertical layouts.
• Optional Vertical AeroDeck adds up to 3 x 120mm or 2 x 140mm fans for GPU cooling.

Build Like Never B4

Co-developed with DAN Cases, the B4-mATX’s modular design unlocks versatile build possibilities. With multiple colour, panel, and layout options, plus an optional accessory, it adapts to a wide range of styles.

• B4-mATX Wood Black
• B4-mATX Mesh White
• B4-mATX Mesh Black (Vertical)
• B4-mATX Wood White (Vertical)
• B4-mATX Wood + Vertical AeroDeck Black
• B4-mATX Mesh + Vertical AeroDeck Black

Note: The Vertical AeroDeck is sold separately.

Compact Design, Broad Compatibility

With a compact 21.3L volume, the B4-mATX delivers impressive hardware compatibility, supporting M-ATX motherboards, 360mm AIOs, 140mm ATX PSUs, and up to 358mm 4-slot GPUs.

Minimal Design, Multiple Styles

The B4-mATX offers a clean mesh panel for an airflow-focused look or a real wood panel for a warmer, refined setup. Both support front-to-back airflow, balancing cooling performance with a streamlined exterior.

Vertical Mode, Maximised Desk Space

The vertical layout improves desk space efficiency by up to 30%. Integrated rear feet allow quick and easy switching between different usage modes.

Note: In vertical mode, the rear clearance for the connector and cable routing is 52mm in total. Please ensure your HDMI / DP cable fits within this space.

Rotatable AC Power Connector

Designed for both horizontal and vertical configurations, the rotatable AC inlet adapts to your setup. Face it outward for convenient cable access, or rotate it inward in vertical mode to avoid clearance limitations.

Note: The power cable is pre-secured to prevent rubbing against the chassis when rotated. Leave the cable tie in place and position the cable before assembly.

Reversible Rear Fan Bracket

The rear fan bracket features a reversible design for greater layout flexibility. It can be installed outward to create more clearance for liquid cooling, or inward to position the fan closer to the CPU airflow path and improve CPU air-cooling performance by up to 1°C.

Note: The rear fan bracket supports standard 120mm fans only.

Recommended Liquid Cooling Configuration

The B4-mATX supports 360mm and 280mm radiators with up to 52mm total thickness.

360 / 280mm AIO Setup

• SFX PSU + M-ATX motherboard
• 3 x Bottom fans
• 2 x Top slim fans (pre-installed)

240mm AIO Setup

• 140mm ATX PSU + M-ATX motherboard
• 3 x Bottom fans
• 2 x Top slim fans (pre-installed)
• 1 x Rear fan

Note: Due to internal space limitations, fans must be installed outwards when using liquid cooling.

240mm AIO Installation Setup

• SFX PSU + M-ATX motherboard
• Bottom fans x3
• Front fan x1
• Rear fan x1
• Top slim fans x2 (pre-installed)

280mm AIO Installation Setup

• SFX PSU + M-ATX motherboard
• Bottom fans x3
• Rear fan x1 / Front fan x1
• Top slim fans x2 (pre-installed)

Note: Due to internal space limitations, fans need to be installed outside the chassis when installing an AIO liquid cooler.

Recommended Air Cooling Configuration

159mm Air Cooler Setup

• SFX PSU + M-ATX motherboard
• 3 x Bottom fans
• 1 x Side fan
• 1 x Rear fan
• 1 x Front slim fan
• 2 x Top slim fans (pre-installed; front fan flipped to intake)

165mm Air Cooler Setup

• 140mm ATX PSU + M-ATX motherboard
• 3 x Bottom fans
• 1 x Rear fan
• 2 x Top slim fans (pre-installed; front fan flipped to intake)

Note: Although the Noctua NH-D15 G2 is officially listed at 168 mm tall, its actual installed height is 165 mm. Additionally, the fans can be mounted 3 mm lower, ensuring compatibility.

Flexible Cooling Configuration

• Top: 2 x 120mm slim fans (pre-installed)
• Side: 3 x 120mm fans / 2 x 140mm fans or 360mm / 280mm / 240mm radiator
• Rear: 1 x 120mm fan
• Bottom: 3 x 120mm fans / 2 x 140mm fans
• Front: 1 x 120mm slim fan

(Note: The front slim fan is not supported with 360mm radiator or ATX PSU installation.)

• 360mm AIO x1
• 120mm Fans x9
• 140mm Fans x4

Pre-installed with two 15mm slim fans. If replacing them with 25mm-thick fans, an SFX power supply is required to ensure sufficient clearance.

Note: To install three 120mm fans, the PCIe accessory below the PCIe slots must be removed.

Note: When installing 140mm fans at the bottom, clearance with the bottom connectors of some mATX motherboards may be limited.

Extra Intake, Better Cooling

Supports a 120 x 120 x 15mm slim front fan with an SFX PSU and GPU under 343mm long, helping improve intake airflow.

Pre-Installed 15mm Slim Fans, Flexible Airflow Design

Two pre-installed 120 x 120 x 15mm slim fans on the top provide enhanced cooling performance. Operating up to 1800 RPM, they are daisy-chained to reduce cable clutter.

• Speed - 0~1800 ±10% RPM
• Airflow - 64.2 CFM
• Static Pressure - 2.4mmH20
• Noise - 30.3dBA

Flexible GPU & Fan Support

Supports up to 358mm long 4-slot graphics cards. Bottom fan support varies by GPU thickness: 2.5-slot GPUs support 25mm fans, 3-slot GPUs support 15mm slim fans, and 3.5-slot or thicker GPUs do not support bottom fans.

Easy GPU Installation

The removable front fan bracket lets large graphics cards slide in from the front side of the chassis for a smoother installation process.

Pre-Installed GPU Anti-Sag Bracket

Built to handle GPUs up to 4 slots thick and 358mm long, the case comes equipped with a dedicated anti-sag bracket to ensure stability and prevent sagging.

Modular Design, Easier Installation

Tool-less removable panels offer quick and easy access for installation and cable routing, while a removable bottom dust filter helps maintain a clean system.

Removable Top Fan Bracket

The removable top fan bracket provides easier access for routing and managing CPU 8-pin cables, while also making it simpler to configure the front-top fan as intake for air-cooler setups.

Easier Cable Management

Cable tie points around the PSU and top brackets help secure CPU 8-pin and PSU cables for a cleaner, more organised build.

• Cable Clip & Tie Point
• Cable Tie Point

In vertical mode, a removable bracket and rotatable cable guide work together to route cables cleanly through the bottom of the case.

Note: 52mm of total desk clearance is recommended for standard HDMI / DP cable routing. Longer connectors may require an adaptor.

Vertical AeroDeck - (Optional Accessory)

In vertical layout, the Vertical AeroDeck enhances GPU cooling while maintaining a cohesive look with the case. It supports up to three 120mm or two 140mm fans, includes a PVC dust filter, and features tempered glass side panels to showcase fan side-frame lighting.

Note: Installation requires repositioning the I/O module.

Thermal Performance Test

Test Configuration (GPU: ROG Astral 5080)	Max / Average Temperature
Without Vertical AERODECK	68.6/66.5°C
With Vertical AERODECK (3 x 120mm fans at 1800 RPM)	64/61.9°C

Flexible Storage Support

Supports 1 x 2.5” SSD at the front, with space at the bottom for either 1 x 2.5” SSD or 1 x 3.5” HDD.

Note: Installing a 3.5″ HDD on the bottom limits GPU thickness to 65mm and supports only one 120mm bottom fan. With a 2.5″ SSD installed, two 120mm bottom fans are supported. This configuration requires the motherboard’s primary PCIe x16 slot to align with the first expansion slot.

Accessible Connectivity

The I/O layout keeps essential ports easy to reach in both traditional and vertical layouts, with a high-speed USB Type-C port supporting up to 20Gbps transfer speeds.

In Collaboration with DAN Cases

Co-developed with Daniel Hansen of DAN Cases, the B4-mATX combines flexible modularity with LIAN LI’s precision craftsmanship in a compact form.

Hard Compatibility

Tool-less removable panels offer quick and easy access for installation and cable routing, while a removable bottom dust filter helps maintain a clean system.

PSU Type	Side AIO	AIO+Fan Thickness Support	MB Support	GPU Length	Rear Fan	Front Fan (15mm slim fan)
ATX PSU	240mm	/	MATX	358mm	120mmx1	/
ATX PSU (Side Mount)	240mm	55mm	ITX	343 / 358mm	120mmx1	120mmx1
ATX PSU (Side Mount)	280mm	52mm	ITX	343 / 358mm	120mmx1	120mmx1
ATX PSU (Side Mount)	360mm	52mm	ITX	358mm	/	/
SFX PSU	240mm	55mm	MATX	343 / 358mm	120mmx1	120mmx1
SFX PSU	280mm	52mm	MATX	343 / 358mm	/	120mmx1
SFX PSU	280mm	52mm	MATX	343 / 358mm	120mmx1 (Alternative to front fan)	120mmx1 (Alternative to rear fan)
SFX PSU	360mm	52mm	MATX	358mm	/	/

Note: When installing a 15mm-thick slim front fan, the maximum GPU length is limited to 343mm. The total thickness of the radiator and fan must not exceed 52mm.