With more than 40 years of proven performance in the field, modified bitumen roofing systems are low-slope roofing workhorses. They’re durable, low-maintenance, budget-friendly and able to take whatever Mother Nature throws at them. And with the membrane and attachment options available, they can be at home on virtually any rooftop.

But how to choose among those options? In this post we’ll talk about the two types of mod bit cap sheet, including how they are different and which applications they are best-suited to. In our next post, we’ll discuss attachment methods.

There are two types of mod bit membrane – SBS and APP. Both are asphalt-based, and in both cases the asphalt is modified with a polymer and reinforced with one or more layers of fabric to create a roofing system that is exceedingly tough and weather-resistant. The polymer used is different, however, making each membrane type better-suited to certain environments.

In SBS membranes, the asphalt is modified with styrene butadiene styrene. They have greater elongation and remain flexible in cold temperatures, helping prevent cracks that can result in leaks. This makes them the right choice for buildings in northern climates where average winter temperatures are lower.

In APP membranes, the asphalt is modified with atactic polypropylene. They have a higher softening point, giving them superior weatherability, puncture resistance, and ability to withstand foot traffic scuffing at elevated temperatures. As a result, APP membranes are the better option for buildings in southern climates where average summer temperatures are much higher.

The next question to ask is how the membrane will be attached. Stay tuned for “Mod Bit – So Many Options (Part 2),” which will address the advantages of self-adhering and torch-applied systems.

Learn more about Mule-Hide Products modified bitumen systems here.

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