The grease resistance of a wide variety of packaging materials was tested before and after creasing and ageing, using a modification of TAPPI method T454m-44. Kraft and sulphite were of little or no value as grease barriers even after paraffin wax coating or impregnating. Vegetable parchment and 'greaseproof' paper were superior to kraft. The grease resistance of glassine was 5 to 10 times greater than that of either greaseproof paper or vegetable parchment. Polyethylene, in turn, was considerably more resistant than glassine, and just slightly less resistant than all grades of "Cellophane", and cellulose acetate, cellulose nitrate, ethyl cellulose, Pliofilm, vinylite, and Saran.Creasing glassine caused large reductions in its grease resistance, especially when heavy basis weights were tested. Paraffin wax coatings seemed to be more effective in improving grease resistance when dense base stocks were used. On kraft, a heavy wax coating was necessary to produce a small improvement, while on glassine only a very light coating was required, to bring about considerable improvement in grease resistance. Ageing many materials at 140° F. markedly reduced their grease resistance. An exception to this was glassine, most samples of which had greater resistance to grease penetration after ageing. Neither ageing nor creasing appreciably affected the grease resistance of Cellophane, or the thermoplastic films tested.