  Gels are used to design bilayered structures with high residual stresses. The
swelling of a thin layer on a compliant substrate leads to compressive
stresses. The post-buckling of this layer is investigated experimentally; the
wavelengths and amplitudes of the resulting modes are measured. A simplified
model with a self-avoiding rod on a Winkler foundation is in semi-quantitative
agreement with experiments and reproduces the observed cusp-like folds.
