Our 3M™ Fire Barrier Block B258 is a pre-formed foam block designed for easy installation to effectively seal larger openings against smoke, toxic gas and flame. It is simple to use and helps reduce sound transmission.

A Better Way to Fill Large Gaps
When sealing larger cavities, use 3M™ Fire Barrier Block B258 to restore the integrity of the wall with a simple "stack, seal, and done" application, without the use of special tools. The blocks are engineered to remain securely in place, eliminating traditional wire mesh reinforcements. Pre-formed blocks help technicians fill large openings quickly. The material is easy to trim on site without special tools, achieving a tight, custom fit. No cure time is required, which means installation is completed faster, and the blocks are paintable with primer for a more seamless appearance.

The blocks are fully re-enterable and reusable, saving time and money, while minimizing waste. Once the opening is filled, seal around the perimeter and any penetrating items with 3M™ Fire Barrier Rated Foam FIP 1-Step or other 3M™ fire barrier sealants (sold separately).
Recommended Applications


Blank openings
Metal pipes
Cables
Cable trays
Insulated pipes, combination penetrations


Fully Tested and Approved
3M™ B258 Fire Barrier Blocks are firestop tested to the criteria of ASTM E 814/UL 1479 Standard Test Method for Fire Tests of Penetration Firestop Systems, ASTM E 84/UL 273 Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM E 90 Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, and ASTM E 413 Classification for Rating Sound Insulation.

Reliable and Affordable Fire Protection
Effective and easy to install, 3M™ Fire Barrier Block B258 are part of our family of fire protection products that offer the broadest, long-lasting solutions for a variety of commercial, industrial and residential applications. As a trusted leader in the fire protection industry, 3M offers a broad line of affordable products designed to meet the most demanding firestop requirements. Find the solution you need from the industry-preferred line of fire protection products.

• Pre-formed foam block maintains tight firestop seal to prevent fire, smoke and toxic gas transmission
• Fits medium to large openings in wall and floor through-penetrations
• No cure time means faster completion
• Block is paintable with primer
• Installation requires no special tools
• Can be repaired and reused as needed, saving time and labor
• Firestop tested in accordance with ASTM E 814/UL 1479
• Can be sealed with 3M™ Fire Barrier Rated Foam FIP 1-Step and other 3M™ fire barrier sealants (sold separately)

• Color: Maroon
• Part Number: FB258
• Product Type: Fire Barrier Block
• Width: 5.12 in