Thermoset membranes incorporate principal polymers that are chemically cross-linked or vulcanized. Membranes that are vulcanized may also be referred to as "cured". One characteristic of true thermoset polymers is that once they are cured, they can only 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, which principally is composed of two compounds, ethylene and propylene, both derived from oil and natural gas. The following are some characteristics of EPDM roof membranes:

  • Sheet widths range from 7.5 ft. to 50 ft. wide.
  • Sheets are typically 45 mils and 60 mils thick.
  • Seams are sealed using liquid adhesives or specially formulated tape.
  • The membranes are typically 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.