This is a three layer sound deadener by Asylum Audio. This product has three layers; Butyl, with a metal layer, topped with a thick foam.

This product helps to insulate the cab from heat and sound. 

This is one large roll which is 10.7 sq ft (19.6"x78.7") of material. 
3mm Foam + 1.5mm Butyl Rubber, Foil .004"