The various kinds of firestop pillows are intended to slow the spread of fire.
They are often used to meet fire-resistance ratings in conduits that need frequent access.
The products are required to have fire-resistance ratings and to be used in accordance with a certification listing.
Batt-based pillows are held in place by compressing them, allowing friction to restrain them.
The foam-based pillows intumesce, swelling as a result of heat exposure.