The Firestop Pillow features a 4-lb density mineral wool compressed between two intumescent sheets, which are encased in a durable polyethylene liner. According to the manufacturer, the pillow has been tested by UL Laboratories, and has been approved for one- and two- hour gypsum wallboard and two-hour concrete block wall assemblies. Other applications include a maximum 4-in. EMT conduit sleeves with data communications cables or up to 24 in. by 5 in. center spine aluminum cable trays containing co-axial power cables, fiber optic cables, and telecommunication cables. The pillow is available in both 1 in. and 2 in. thicknesses.