Modified asphalt membranes are often layered into 2-3 plies to achieve desired performance, budget, or warranty needs. These combinations typically include a base layer (base sheet) and a top layer (cap sheet), and in many circumstances one or more middle layers (ply sheets). Given the versatile nature of modified roofing, base sheets can often be used as ply sheets, and vice versa.

The top layer of multi-ply arrangement is called the cap sheet. It often varies slightly from base and ply sheets most noticeably because it is often topped with granules for extra impact resistance and UV protection.