The use of a composition based on silicon dioxide as antiblocking agent is described which is characterized in that it has silicon dioxide having a particle size of 2 to 8 .mu.m, a specific surface of 150 to 850 m.sup.2 /g and a specific pore volume of 1.4 to 2.0 ml/g which has been treated with polyol. This silicon dioxide can be used together with a slip agent as combined antiblocking agent and slip agent. The working-in of the antiblocking agent or of the combined antiblocking agent and slip agent into a polymer is preferably in the form of a masterbatch. A preferred antiblocking agent contains as polyol ethoxylated pentaerythritol in which the pentaerythritol/ethoxy ratio lies in the range from 1:0.5 to 1:25. The antiblocking agent can be obtained by micronizing silicon dioxide to the given particle size and impregnating it with the polyol.