Page "Vulcanization" Paragraph 2

Uncured natural rubber is sticky, deforms easily when warm, and is brittle when cold.

In this state, it is a poor material when a high level of elasticity is required.

The reason for inelastic deformation of un-vulcanized rubber can be found in its chemical structure: rubber is composed of long polymer chains.

These chains can move independently relative to each other, which lets the material change shape.

Crosslinking introduced by vulcanization prevents the polymer chains from moving independently.

As a result, when stress is applied the vulcanized rubber deforms, but upon release of the stress, the article reverts to its original shape.