Tensile and water vapor permeability properties of sodium caseinate based films were studied to optimize film composition in terms of kind and ratio of plasticizer (glycerol and sorbitol) and lipids (oleic acid and beeswax). Glycerol was more effective as plasticizer than sorbitol in the caseinate matrices; films with 90% sorbitol had similar tensile properties to those elaborated with 40-50% glycerol. Oleic acid, pure or mixed with beeswax, has a plasticizing effect in the films, increasing their elasticity, flexibility and stretchability, and reduces water vapor permeability with respect to sodium caseinate films. The films with a 1:0.3:0.5 protein: glycerol: lipid ratio containing a 70:30 OA:BW ratio were the ones which showed the most adequate functional properties if both tensile and water transport properties are taken into account (Elastic Modulus: 29.01 +/- 9.36 MPa, Elongation at break: 23.90 +/- 2.05, water vapor permeability (WVP): 1.8 +/- 0.2 g mm/kPa h m(2)). Although the best water vapor permeability properties were obtained for films without glycerol (WVP: 0.63 +/- 0.07 g mm/kPa h m(2)), no adequate tensile properties were obtained in these cases. (c) 2007 Elsevier Ltd. All rights reserved.