Rubber is an interesting material possessing some remarkable properties, the most important of which is its high elastic extensibility. Ordinary solids, such as metals, nonmetallic crystals, and glasses, can be deformed or strained elastically only to a small extent, corresponding to an extension of the order of 1%. If an attempt is made to apply a greater extension, they either break, as in the case of glass, or deform plastically, like lead.