(nitroso rubber). A flame and heat-resistant copolymer derived from trifluoronitrosomethane (CF3NO) and tetrafluoroethylene (F2C═CF2). A third monomer (methyl-4-nitrosoperfluorobutyrate) provides more easily cross-linked functional groups than heretofore available. This terpolymer, called nitroso ester terpolymer (NET), is a notable improvement on the earlier copolymer and is especially effective for fireproof interiors of aerospace vehicles and airplanes. Cross-linking is by a peroxide mechanism. Properties of the terpolymer are a glass transition temperature of approximately −50C, decomposition temperature of 275C, tensile strength 750 psi, elongation 500%, Shore hardness 78. Nonflammable.