Which material is specifically designed to fill gaps in firestop systems during a fire?

Intumescent strips are specifically designed to fill gaps in firestop systems during a fire. These materials expand significantly when exposed to high temperatures, effectively sealing off openings and preventing the spread of fire and smoke through walls, floors, and ceilings. The expansion of the intumescent material closes off the gap, which is vital in maintaining the integrity of fire-rated assemblies, thereby enhancing overall fire safety.

Other materials, while they may serve different purposes, do not provide the same level of firestop protection. Fiberglass insulation is primarily used for thermal insulation and soundproofing, rather than as a firestopping option. Metal sheets can offer some fire resistance but are not designed to fill gaps dynamically in the same way that intumescent strips are. Cement board is used for fire-resistant construction but does not expand to fill gaps during a fire. Therefore, the unique properties of intumescent strips make them the correct choice for effective firestopping.