Thermoset membranes incorporate principal polymers that are chemically cross linked or vulcanized. Membranes that are vulcanized also may be referred to as “cured.” One characteristic of true thermoset polymers is once they are cured, they only can be bonded to simliar materials with adhesives.

There are five common subcategories of thermoset roof membranes:

  • Ethylene propylene diene terpolymer (EPDM)
  • Chlorosulfonated polyethylene (CSPE)
  • Epichlorohydrin (ECH)
  • Neoprene (CR)
  • Polyisobutylene (PIB)

The most common thermoset roof membrane is EPDM. EPDM principally is composed of two compounds, ethylene and propylene, that are derived from oil and natural gas. The following are some characteristics of EPDM roof membranes:

  • Sheet widths range from 7.5 feet to 50 feet wide.
  • Sheets are typically 45 mils and 60 mils thick.
  • Seams are sealed using liquid adhesives or special formulated tape.
  • The membranes commonly are black, but white is available.

EPDM roof membranes can be installed fully adhered, mechanically attached (using batten bars) or ballasted. Most EPDM membranes do not receive surfacings.

EPDM and polymer-modified bitumen membranes often are confused by consumers because of colloquialisms used by roofing contractors. Contractors commonly call both of these membranes “rubber” roofs. However, in most cases, when contractors specify rubber roofs, they are referring to EPDM.