Metacaulk® Firestop Pillows are intumescent and designed for use primarily in large openings with cables, cable trays, blank openings or multiple penetrating items.Metacaulk® Firestop Pillows are intumescent and designed for use primarily in large temporary or frequently accessed openings with cables, cable trays, blank openings or multiple penetrating items. In the event of a fire, Metacaulk® Firestop Pillows will prevent the spread of flames and hot gases through the openings. UL Classified systems up to 4 hours • Easy to install / No tools required Cost effective - Reusable Forms a very strong char No wire mesh required in most installations Two sizes