Products / LayfastSBS

LayfastSBS is MBTechnology's fiberglass-reinforced SBS modified roof underlayment, mechanically fastened in place of 30 and 40 lb felt under shingle, tile, shake and metal roofs, and also used as a base sheet. It comes in three weights, TU35, TU43 and TU70, in 39-3/4 inch rolls coated on both sides with a fine mineral parting agent. ICC-ES report ESR-2799 (reissued July 2024) recognizes it as an alternative to ASTM D226 Type I and Type II underlayment on slopes of 2:12 and greater. The product page states it meets the requirements of a Class A fire rating under ASTM E108 / UL 790, and MBTechnology lists 10, 15, 20 and 30 year limited material warranties that depend on the TU weight and number of layers.