DuraWeld 4M APP is a durable granule surfaced, premium APP (Atactic-Polypropylene) torch applied membrane. Manufactured with a strong non-woven polyester mat that is saturated and coated with a premium quality, nonblown asphaltic bitumen and APP resins for a durable, heat resistant, flexible and easily maintainable membrane. It is designed for use as a cap sheet in modified bitumen roof systems.