The present invention provides an additive comprising A) a copolymer of ethylene and 8-21 mol % of at least one acrylic or vinyl ester having a C1-C18-alkyl radical and B) a comb polymer containing structural units of B1) at least one olefin as monomer 1, which bears at least one C8-C18-alkyl radical on the olefinic double bond, and B2) at least one ethylenically unsaturated dicarboxylic acid as monomer 2, which bears at least one C8-C16-alkyl radical bonded via an amide and/or imide moiety, wherein the sum Q Q = ∑ i ⁢ w 1 ⁢ i · n 1 ⁢ i + ∑ j ⁢ w 2 ⁢ j · n 2 ⁢ j of the molar averages of the carbon chain length distributions in the alkyl radicals of monomer 1 on the one hand and the alkyl radicals of the amide and/or imide groups of monomer 2 on the other hand is from 23 to 27, where w1 is the molar proportion of the individual chain lengths in the alkyl radicals of monomer 1, w2 is the molar proportion of the individual chain lengths in the alkyl radicals of the amide and/or imide groups of monomer 2, n1 are the individual chain lengths in the alkyl radicals of monomer 1, n2 are the individual chain lengths in the alkyl radicals of the amide and/or imide groups of monomer 2, i is the serial variable for the individual chain lengths in the alkyl radicals of monomer 1, and j is the serial variable for the individual chain lengths in the alkyl radicals of the amide and/or imide groups of monomer 2.