Abstract: A process for flash-spinning a web of plexifilamentary film-fibril strands of synthetic fiber-forming polymer and laying down the web to form a nonwoven batt material therefrom is provided. The process includes the the step of generating a spin fluid consisting essentially of synthetic fiber-forming polymer and a spin agent, wherein the spin agent is comprised of at least 80% by weight, based on the total weight of the spin agent, of hydrocarbons comprised substantially exclusively of carbon and hydrogen atoms. The hydrocarbons are comprised of at least 25% by weight of unsaturated hydrocarbons having 4-8 carbon atoms.