You don’t need to be an engineer to know that all construction materials expand or contract with fluctuations in temperature. Due to the composition of polyvinyl chloride (PVC), these temperature changes affect PVC more than traditional materials such as steel or aluminum. Thermal expansion and contraction have a very significant effect on long straight runs of conduit. For this type of application, expansion fittings are used to accommodate changes in length. Expansion couplings help prevent the potentially harmful thermal stresses in the conduit or in any supporting structures.