The influence of molecular architecture on the rapid crack propagation (RCP) resistance of a wide variety of high-density polyethylene pipes was investigated. It was concluded that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important architectural attributes for RCP resistance. The ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the RCP resistance of the resultant pipes.