A composition for an insulating layer of an electric cable wherein the composition contains an ethylene plastic as the base resin and further contains up to about 5% by weight of additives including antioxidant, and peroxide cross-linking agent. The composition is characterised in that the antioxidant additive includes a compound of the formula (V): R1(—(C+O)O—)k(CH2)1—S—(CH2)m(—OO(C═O)—)nR2 where R1 and R2, which are the same of different, are C7-C23 alkyl, C7-C23 alkenyl, R3—Ar—, Ar—R3—, or AR—, where R3 is C8-C24 alkyl and Ar is c6-c14 aryl; k and n, which are the same of different, are 0 or 1, l and m, which are the same or different, are integers ≧0; with the proviso that the compound is free from phenolic groups; and that the compositions is free from compounds having the formula (VI): R—O—(C═O)—CH2CH2SCH2CH2—(C═O)—O—R where R is a C8-C20 alkyl group.