Thermal shock is a method of environmental testing that subjects a product to alternating extremes of high and low temperatures. 

Thermal shock testing allows for the observation of changes in product characteristics and failure occurrence caused by different materials and their thermal expansion coefficients. This differential expansion can be understood in terms of stress or of strain, equivalently. 

Thermal shock and thermal stress chambers are designed to operate in accordance with reliability programs, quality control, commercial test programs and military tests including MIL-STD 202, 883, 810 and JEDEC.