A one-pack polymer modifier containing a) at least one process aid functionalized with a reactive epoxy, hydroxyl, β-keto ester, β-keto amide or carboxylic acid functional group, b) at least one impact modifier, c) optionally, at least one mineral filler and d) optionally, at least one further additive is useful for modifying the properties of thermoplastic polymers such as PVC, including reducing the surface gloss of an article prepared from the thermoplastic polymer and improving the impact strength of such an article.