hard rubber exhibits shape-memory effect and can be fairly easily reshaped within certain limits. Depending on the sulfur percentage hard rubber has a thermoplastic transition or softening temperature of 70 to 80 °C.

The material is brittle, which produces problems in its use in battery cases for example, where the integrity of the case is vital to prevent leakage of sulfuric acid. It has now been generally replaced by carbon black-filled polypropylene.