This study examined the effect of the tielayer thickness on the delamination behavior of polypropylene/tie-layer/nylon 6 multilayers. Various maleated polypropylene resins were compared for their effectiveness as tie-layers. Delamination failure occurred cohesively in all the multilayer systems. Two adhesion regimes were defined according to the change in the slope of the linear relationship between the delamination toughness and the tie-layer thickness. The measured delamination toughness of the various tie-layers was quantitatively correlated to the length of the damage zone that formed at the crack tip. In addition, the effect of the tie-layer thickness on the multilayer tensile properties was correlated with the delamination behavior. The fracture strain of the multi-layers decreased with decreasing tie-layer thickness. An examination of the prefracture damage mechanism of the stretched multilayers revealed a good correlation with the delamination toughness of the tie-layers. In thick tie-layers (>2 mu m), the delamination toughness was great enough to prevent the delamination of the multilayers when they were stretched. In thin tie-layers (<2 mu m), the delamination toughness of all the tie-layers was low; consequently, delamination led to premature fracture in the stretched multilayers. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:1999-2012, 2011