Thermally imagable elements are described comprising on a substrate with hydrophilic surface (a) a first layer comprising a first polymer soluble or swellable in aqueous alkaline developer and insoluble in organic solvents with low polarity and (b) a second layer comprising a second polymer soluble or swellable in aqueous alkaline developer, wherein the first polymer is different from the second polymer and the second polymer comprises vinyl acetal repeating units and pendant acidic groups selected from COOH, —SO3H, —PO3H2, —PO4H2, aromatic OH and groups having acidic amide or imide groups.