Firestone MB Base Sheet is high-performance roofing base sheet, which is asphalt impregnated & coated and has a glass fiber mat reinforcement. It has been designed to give superior durability and ease of installation in asphalt roofing systems. Firestone MB Base Sheet may be used as a base ply in SBS, APP Modified Bitumen and Built-Up Roofing Systems. By using only pure roofing grade asphalt, with little or no fillers, Firestone MB Base Sheet offers better flexibility and workability than typical heavily filled base sheets.