4" Type B for smaller aircraft such us Cessna 150,152 Piper Cherokee, Warrior etc.overall dimensions 15" X 15" made of Dupont Cordura 1000 deniers 2lb non flammable foam (firm) the back is 2" thick with a 3" lumbar area it comes with straps to secure the cushion to the back of the seat that when no in use serve as carrying handles.