Expansion Joint and Joint Sealant Glossary Index:

- Adhesion in Tension

- Blockout

- Compression Set

- Continuity of Seal

-  Expansion Joint

- Nosing Material

- Non-Invasive Anchoring

- Split Slab

- Sound Transmission Class (STC)

- Thermal Shock

Expansion Joints--Terms and Terminology: COMPRESSION SET

Compression set is the permanent loss of the ability to self-expand that results after a material is subject to normal compression cycles.  Compression set is made worse by simultaneous exposure of certain materials to heat. 

Impregnated, open-cell, foam is used as the backing for precompressed sealants because it features very low compression set.

Closed-cell foams suffer on average 25% permanent compression set under movement and temperature cycles typical in construction applications.