What is rubber swelling? If elastomers remain in certain liquid or gaseous media for a longer period of time, the properties of the rubber can change depending on the material. The most noticeable change can be seen in the volume or mass. However, a change in tensile strength and Shore hardness can also occur. Depending on the extent of the deviation, rubbers are classified as resistant or non-resistant. A negative change in volume is also referred to as shrinkage. Swelling occurs when the swelling medium penetrates the material and forces the polymer chains of the elastomer apart. Higher temperatures accelerate this process as the molecules move faster. Although rubber hardly swells in water, it swells strongly in inorganic solvents and oils, as these can penetrate the structure of the rubber more easily. In particular, petrol and aromatic hydrocarbons such as toluene cause common rubbers such as natural rubber (NR), nitrile rubber (NBR) and styrene-butadiene rubber (SBR) to swell. NBR is also susceptible to acetone and alcohols. EPDM, silicone and fluororubber are considered to be more resistant rubbers; they do not swell as much as conventional types of rubber.