Compositions comprising: A. Ethylene-based polymer, e.g., LDPE; B. Polyalkylene glycol, e.g., PEG; C. Tertiary hindered amine stabilizer; D. Sulphur-containing hindered phenol antioxidant; E. Peroxide; and F. Optional coagent are useful in the preparation of TRXLPE insulation for medium voltage cable that exhibits a commercially desirable balance of long term heat aging retardancy and water-tree resistance.