Modified open-cell foams with a density in the range from 5 to 1000 kg/m.sup.3 and with an average pore diameter in the range from 1 .mu.m to 1 mm, comprising an amount in the range from 1 to 2500% by weight based on the weight of the unmodified open-cell foam, of at least one polymer which is solid at room temperature and which contains carboxy groups and/or which contains carboxylic ester groups, and which has a molar mass M.sub.n in the range from 1000 to 1000 000 g/mol.