During drying of a chemically crosslinked poly(vinyl alcohol) gel, we observed, by atomic force microscopy (AFM) and scanning electronic microscopy, micron-order wrinkling which remains until the end of drying. We show that while at high humidity drying is homogeneous and no surface instability is observed, fast drying at low humidity induces the formation of a glassy skin layer on the soft bulk that wrinkles because the skin is compressed as the bulk contracts. The role of the glass transition is not only to create a mismatch of the elasticity with the bulk but also to remove the in-plane tensile tension which stretches the skin before drying. We proved experimentally the presence of this thin glassy skin on the wet bulk by approach–retract curve measurements in AFM. We also comment on the effect of mechanical restraint and the observation of hierarchical wrinkling over different length scales.