Infra‐red absorption spectra of polythene, rubber, polystyrene and polyvinyl chloride have been obtained at 4° absolute, in the rocksalt region, in a specially designed transmission cell containing liquid helium. No unusual changes occur on cooling which considerably alter the absorption. Some sharpening and improvement in resolution occurs, but the widths of most bands in polymers remain wide.In polythene one component of the doublet at 720 cm−1becomes very sharp (possibly even less than the experimental value of the slit width, 1 cm−1). Its companion remains broad, about 4 cm−1. The two components are interpreted as CH2wagging intrans‐ andcis‐configurations of the hydro‐carbon chain.