Page "Natural rubber" Paragraph 22

When cooled below the glass transition temperature, the quasi-fluid chain segments " freeze " into fixed geometries and the rubber abruptly loses its elastic properties, although the process is reversible.

This is a property it shares with most elastomers.

At very low temperatures, rubber is rather brittle ; it will break into shards when struck or stretched.

This critical temperature is the reason winter tires use a softer version of rubber than normal tires.

The failing rubber o-ring seals that contributed to the cause of the Challenger disaster were thought to have cooled below their critical temperature ; the disaster happened on an unusually cold day.