Stress‐temperature (constant strain) and length‐temperature (constant stress) measurements have been made on Paracril‐35 (a butadiene‐acrylonitrile copolymer) in the temperature range −80°C to 25°C, which includes the glass‐like, transition, and rubber‐like states for this material (Tg∼−25°C). Time effects are observed in the transition region, but for temperature gradients used (down to about 1°C in 4 hours) the behavior at low temperatures is unique, indicating the existence of a real transition. This behavior is independent of the strain imposed at room temperature. The shift in transition temperature (in the length‐temperature work) with extension is found to give quantitative support to the theory that the transition occurs at a certain minimum volume. In the rubber‐like region, behavior is represented by the usual equation of state.