Deformation by laundering is investigated for single jersey and 1 × 1 rib flat knit silk and cotton fabrics with yams of varying linear densities and fabric tightness. The fabrics are subjected to relaxation processes and an extended series of wash and tumble- dry cycles. Changes in dimensions are measured in every process and cycle. Statistical analyses of the experimental data reveal the effect of yam type as well as linear density and tightness factor on the linear and area shrinkage behavior of silk as compared to cotton. Cotton shrinks more than silk, and silk rib knits stretch excessively in width. Silk attains full relaxation after one laundering cycle. Microscopic views reveal the appearance of ball-like formations along silk fibers after repeated laundering. It is possible to predict fabric dimensional changes with wet relaxation as well as with laundering, especially in silk.