Abstract –The curing contraction of addition‐type silicone impression materials was measured by the mercury bath method. The results point to a classification of this group of materials into the following two types: 1: materials with maximum 0.08% polymerization contraction at 22°C 15 min after mixing and maximum 0.03% contraction at 22°C during storage from 15 min to 24 h (Permagum®, President®, Reflect® and Reprosil®). 2: materials with more than 0.08% polymerization contraction at 22°C 15 min after mixing and significantly more than 0.03% contraction during storage at 22°C from 15 min to 24 h (Exaflex®