AbstractThe interlaminar shear strength of reinforced plastic composites has long been recognized as a critical property in the structural performance of composites. However, its role in structural performance and the many factors that influence it have not been clearly elucidated. Although much attention has been given to the importance of resin‐glass adhesion, little is known regarding the contribution of resin strength and composite quality. In this article it is shown that interlaminar shear strength is a direct function of both resin strength and composite void content. The curves of resin tensile strength vs interlaminar shear strength indicate a limiting value for interlaminar shear above which increases in resin tensile strength do not increase defects.