Expandable—If a fire breaks out, they expand to seal any remaining gaps.

Cut-to-Size—Cut-to-size blocks can be customized to fill odd-shaped openings. They expand in all directions when exposed to flames, so you can cut them without reducing their fire protection.

Hook and Loop Attachment Strips—Blocks with hook and loop attachment strips can be locked together or taken apart easily, so they're good for creating temporary barriers. Their cover expands in two directions when exposed to flames. Do not cut these blocks, or they will lose their shape and fail to stop fire and smoke.

Flammability Rating—These blocks are tested to ASTM and UL standards for stopping the spread of smoke and flames.