The Inter-Ply Felts illustrated in (Figure I - green dot) are bound together as a single layer of asphalt and porous felt. This is a manufacturing process where the felts are interwoven during installation to create the roof Membrane (Figure II).

The implementation of ISO Standards ( International Organization for Standardization ) are rare in roofing because the industry is dominated by much smaller companies where such management techniques are less known. Instead, roofers tend to use Generally Accepted Roofing Practices (GARP).