Expansion coupling are devices with at least one bellow or airtight chamber, that absorb movement, stress, noise and vibration to protect pipe or duct fittings. They allow for rigid mounting of pipes in constricted areas and eliminate more complicated means of protecting piping from changes. The joints, made usually of rubber or plastic, are manufactured in various sizes to accommodate different pipe and duct sizes.

Expansion joints or couplings connect sections of pipe and provide allowance for movement due to service load, shock, or thermal cycles. They may have solvent weld socket ends or female threaded ends. The flexible component of an expansion joint is called "bellow"and is typically constructed of materials that have high ductile strength to withstand the stresses of deflection. Often, a bellows expansion joint can withstand thousands of deflection cycles without breaking.

Expansion joints provide a wide range of deflection capability. A flexible expansion joint may be designed to deflect lateral, axial, angular, or torsional stresses, or a combination of any of these. Some of the expansion joints with a varying deflection capabilities are hinged expansion joints, gimbals and universal expansion joints and elbow expansion joints.

Some of the popular types of expansion joints (on the basis of material used in manufacturing) are: