The CoreFlex composite waterproofing membrane consists of a reinforced thermoplastic membrane integrally bonded to a proprietary active polymer core (APC) layer for waterproofing protection. While conventional PVC membranes rely solely on welds to prevent water intrusion at overlap seams, CoreFlex membrane overlap seams use both a conventional weld and an overlap assembly of the APC technology to ensure water tightness and eliminate the reliance of seam integrity strictly on installation labor. CETCO Building Materials Group. 800-527-9948.