The present invention relates to a polymer composition comprising a polyolefin, peroxide and a sulphur containing antioxidant, wherein said peroxide is present in an amount which corresponds to X mmol —O—O—/kg polymer composition and said sulphur containing antioxidant is present in an amount which corresponds to Y mmol —OH/kg polymer composition, wherein Y1≦Y≦Y2, X≦45 and 0.9*Y+m≦X≦n−k*Y, wherein Y1 is 0.50 and Y2 is 10, and m is 0.8, n is 70 and k is 4.7; and wherein said polymer composition has a melt flow rate (MFR) of less than 1.7, and said polymer composition comprises less than 0.05% by weight (wt %) 2,4-Diphenyl-4-methyl-1-pentene; a crosslinked polymer composition, and use thereof, a power cable insulation, a power cable, useful in high voltage (HV DC) and extra high voltage (EHV DC) direct current applications, and a method for reducing electrical conductivity of a crosslinked polymer composition.