Linear coefficient of thermal expansion of metal used for metal ceramic restoration range from:

Most porcelains have coefficients of thermal expansion between 13.0 and 14.0 × 10 −6 /°C, and metals between 13.5 and 14.5 × 10 −6 /°C. The difference of 0.5 × 10 −6 /°C  in  thermal  contraction between metal and porcelain causes the metal to contract slightly more than does the ceramic during cooling. This condition places the porcelain under slight residual compression, which makes it less sensitive to the tensile stresses induced by mechanical loading. Craig’s Restorative dentistry 14 ed page 222