The present invention relates to a composition comprising (i) a crosslinkable polyolefin with hydrolysable silane groups (A), (ii) a silanol condensation catalyst (B) of the formula Ar(SO3H)x as defined herein, and (iii) a silicon containing compound (C) selected from the group consisting of 3-ureidopropyltrimethoxysilane, N-trimethoxysilylmethyl-O-methylcarbamate, and mixtures thereof; to an article, in particular a wire or cable, comprising such a composition, and to the use of such a composition for producing the article. The present invention further relates to the use of silicon containing compound (C) as a processing aid in the compounding of polyolefin compositions and as a surface smoothening agent in polyolefin compositions. Finally, the present invention relates to the use of a silicon containing compound (C) as a drying agent for polyolefin compositions, as a corrosion inhibitor in polyolefin compositions comprising a Bronsted acid and as a pH controlling agent in polymer compositions comprising a Bronsted acid.