Aqueous binders for granular and/or fibrous substrates comprising as active constituents: a) at least one polymer which is obtainable by free-radical addition polymerization and comprises in copolymerized form ≧5.5% and ≧20% by weight of an α,β-ethylenically unsaturated monocarboxylic or dicarboxylic acid [polymer A], b) at least one polymer which is obtainable by free-radical addition polymerization and comprises in copolymerized form ≧40% by weight of an α,β-ethylenically unsaturated monocarboxylic or dicarboxylic acid [polymer B], and c) at least one polyol compound having at least two hydroxyl groups [polyol C].