In this paper, we describe nano-assembly of amphiphilic polyelectrolytes within alummosilicate nanoplates by layer-by-layer deposition and demonstrate how the resulting films are capable of functioning as hydrophobic barrier. The polyelectrolytes with a rigid backbone and long alkyl substitutes organized within the inorganic nanosheets, to form a double layer of interdigitated alkyl substitutes. The resulting 100 nm-thick hydrophobic barriers efficiently blocked transport of moisture and hence enhanced the water vapor barrier properties of a relatively thick substrate (Nation membrane, ca. 50 mu m) up to 22 times. (c) 2005 Elsevier B.V. All rights reserved.