Polymer composition comprising a) 10-99.99% by weight of at least one polyolefin, b) 0-50% by weight of a thermoplastic that is not a polyolefin, c) 0.005-1% by weight of per se known polymer additives, as well as an additional component chosen among d) at least one polybranched organic/inorganic hybrid polymer which has an inorganic core carrying organic branches, the core and branches forming a particulate structure, or/and e) a fat-soluble metal compound prepared by reacting a metal salt and an acidic, organic compound in a process in which a suitable oxidation agent ensures that all the metal in the end product is present in its highest stable oxidation state at standard conditions (25° C. and maximum 98% humidity).