The invention provides an insulation composition for electric cable comprising (a) a base polymer comprising polyolefin, (b) an additive comprising a blend of; (i) at least one amine antioxidant, and (ii) at least one hindered amine light stabilizer, and (iii) polyethylene glycol. The composition may optionally comprise an antioxidant mixture of (i) at least one fast radical scavenger selected from the group consisting of: low hindered phenols, low hindered thiophenols, low hindered thiobisphenols, aliphatic amines, aromatic amines, NOR HALS, hydroxylamines, and mixtures thereof; and (ii) at least one long term stabilizer selected from the group consisting of: low hindered phenols, highly hindered phenols, thiosynergists, aliphatic amines, aromatic amines, HALS, hydroxylamines, and mixtures thereof. Surprisingly these antioxidants and radical scavengers give improved tree resistance over other combinations known in the art.