Temperature affects the elasticity of elastomers in an unusual way. When the elastomer is assumed to be in a stretched state, heating causes them to contract. Vice versa, cooling can cause expansion. This can be observed with an ordinary rubber band. Stretching a rubber band will cause it to release heat, while releasing it after it has been stretched will lead it to absorb heat, causing its surroundings to become cooler. This phenomenon can be explained with the Gibbs free energy. Rearranging Δ G =Δ H − T Δ S, where G is the free energy, H is the enthalpy, and S is the entropy, we obtain T Δ S = Δ H − Δ G. Since stretching is nonspontaneous, as it requires external work, T Δ S must be negative. Since T is always positive (it can never reach absolute zero), the Δ S must be negative, implying that the rubber in its natural state is more entangled (with more microstates) than when it is under tension. Thus, when the tension is removed, the reaction is spontaneous, leading Δ G to be negative. Consequently, the cooling effect must result in a positive ΔH, so Δ S will be positive there.