Elastomeric materials and methods of producing them comprising: A. About 50-90 percent by weight of a base elastomeric composition as a ''''backbone'''' or main component formed by copolymerizing a mixture comprising 1. ABOUT 75-99.9 PERCENT BY WEIGHT OF THE BASE COMPOSITION OF AT LEAST ONE MONOMER POLYMERIZABLE TO GIVE A RUBBERY POLYMER AND SELECTED FROM THE GROUP CONSISTING OF ALKYL (C2-C8) acrylates, and mixtures thereof with each other and with up to an equal weight amount of ethylene, propylene, or isobutylene; and 2. AT LEAST ABOUT 0.1 PERCENT BY WEIGHT OF THE BASE COMPOSITION OF AT LEAST ONE ETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLE WITH (A)(1) and containing at least one radical effective to crosslink said base composition by a reaction which is activated separately from the polymerization reaction; and B. About 50-10 percent by weight of a reinforcing material for the base composition and dispersed throughout the base composition consisting of a polymer of 1. AT LEAST ONE HALOGEN MONOMER SELECTED FROM THE GROUP CONSISTING OF VINYLIDENE CHLORIDE, VINYLIDENE FLUORIDE, VINYLIDENE FLUOROCHLORIDE, VINYL CHLORIDE AND VINYL FLUORIDE; AND 2. UP TO ABOUT 6 PERCENT BY WEIGHT OF THE MIXTURE OF AT LEAST ONE Alpha , Beta -MONOETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLE WITH (B)(1). The backbone is crosslinked by virtue of the reaction of the radicals in monomer (A)(2) to make the backbone solvent insoluble. The backbone may optionally contain a diluent and/or a hardener, the latter being a monomer effective to raise the glass transition temperature of the copolymer. Preferably, the elastomers are spun into fibers or extruded into films. This application is a continuation-in-part of Ser. No. 372,476 filed June 4, 1964.