Whey protein isolate (WPI)-based composite films with three different types of nano-clays. Cloisite Na(+) Cloisite 20A, and Cloisite 3013, were prepared using a solution casting method, and their physical and antimicrobial properties were determined in order to better understand the effect of nano-clay type on film properties. The resulting films exhibited an opaque appearance and haze, and the degree of this effect depended on type of nano-clays added. However, these films displayed a similar gloss and slightly lower transparency relative to transparent neat WPI film. The type of nano-clay used significantly influenced the tensile and the water vapor barrier properties of the composite films with the exception of Cloisite 30B, which had no negative effect. In addition, the WPI/Cloisite 30B composite films showed a beneficially bacteriostatic effect against Gram-positive bacteria, Listeria monocytogenes. (c) 2008 Elsevier Ltd. All rights reserved.