What type of material is called intumescent putty?

Intumescent putty is a sealing material specifically designed to provide fire protection by expanding when exposed to heat. This unique characteristic allows it to fill gaps and openings in fire-rated walls and floors, effectively preventing the passage of smoke and flames during a fire event. When heated, the putty swells and forms a char layer that can block fire and hot gases, thus maintaining the integrity of the fire-rated assembly.

Other materials mentioned, such as fire-resistant sprays or delayed ignition coatings, serve different functions in fire protection. They do not possess the same expansion properties as intumescent putty and are not specifically designed for sealing openings during a fire. Intumescent putty is crucial for maintaining the fire resistance of penetrations, making it essential in firestop systems.