What is rubber and why does it stretch ?

The terms Elastomer and Rubber are scientifically identical and inter changeable , although the letters used in some are as to refer only to natural rubber which comes from the latex contained by some trees and other plants as opposed to synthetic rubber which is generally an oil by product.

Some standards attempt to reserve the term elastomer for a cross linked material. Elastomer’s are a class of materials which differ quite obviously from all other solid materials in that they can be stretched easily and almost completely reversibly, to high extensions. An ordinary postal rubber band illustrate this behaviour. It will generally be made from natural rubber, and can be stretched to seven times its original length, after which – before reaching its ultimate breaking elongation –it can be released and will rapidly recover to almost exactly the original length that it had before stretching.

The material is said to be elastic. Most synthetic elastomers are not as elastic as natural rubber, but all can be stretched or other vice deformed in a reversible manner to an extent which easily distinguishes them from all other solid matrials. A metal spring exhibits a high reversible elasticity, but this is a feature of its wound shape. The actual metal itself of which the spring is made only deforms slightly, by twisting locally, of any particular point, nothing like the high deformation of which elastomers are capable.