Modified bituminous (Polymer-modified bitumen) roof membranes continue to be popular option for low-sloped roofs due to their proven performance. Historically these products have been torch-applied, mop-applied using hot asphalt (SBS only), or applied with solvent-based adhesives.

Polymer-modified bitumen sheets are made with polyester and/or glass-fiber reinforcements. Most manufactures of Mod/Bit produce material with reinforcements that are filled, saturated or coated with very fine minerals, such as sand, mica or talc. All polymer-modified bitumen coated sheets are factory-coated on one or both sides with modified bitumen. The sheets are surfaced on one or both sides with very fine minerals, such as sand, mica or talc. The polymer-modified bitumen sheets are produced in a variety of weights and with a variety of reinforcements. Many smooth-surfaced sheets are used as base sheets, interply sheets and top ply sheets in multiple-ply mod bit membranes. Granule-surface and metal-foil laminate sheets generally serve as cap and flashing sheets.