Elongation is the percentage increase of the original length of a rubber sample, as a result of tensile force being applied to the sample itself. Elongation is inversely proportional to hardness, tensile strength, and modulus. That is, the greater a material’s hardness, tensile strength, and modulus, the less it will elongate under stress.
It takes more force to stretch a hard material having high tensile strength and high modulus, than to stretch a soft material with low tensile strength and low modulus. Ultimate elongation is the elongation at the moment the specimen breaks. Generally is noted along with tensile strength and modulus during tensile testing. Some elastomeric materials are much more forgiving in this area than others. Natural rubber can often stretch up to 700% before breaking. Fluorocarbons typically rupture is at about 300%.