What does "APP" stand for in BUR material types?

The term "APP" in the context of built-up roofing (BUR) materials stands for Atactic Polypropylene. This type of polymer is utilized in roofing membranes because of its beneficial properties, such as flexibility, durability, and resistance to UV radiation. Atactic Polypropylene has a lack of a crystalline structure, which contributes to its advantageous characteristics for roofing applications, particularly its ability to maintain performance under varying temperatures and conditions.

In roofing, membranes made with APP are often used in modified bitumen systems, where they can provide strong waterproofing capabilities and enhanced energy efficiency. The proper selection of APP as a material type is crucial for ensuring the longevity and reliability of the roofing system, making it a popular choice among roofing professionals.