Copolymer of ethylene and an alpha-olefin, having a density>0.930 g/cm3,melt index (g/10 min)>4, molecular weight distribution (MWD)>3.0, and FNCT>250 hours. The copolymer is suitable for use in rotomolding applications. The copolymer possesses improved impact strength, improved permeation resistance and improved environmental stress crack resistance and may suitably be prepared by use of metallocene catalysts.