DuPont™ Elvaloy® Ketone Ethylene Ester (KEE) is a solid, flexible, high-molecular ingredient ideal for thermoplastic processing. So, where does KEE come in? Well, conventional plasticizers are liquids, whereas KEE is a very soft, flexible solid polymer. So, if you used KEE instead of a liquid plasticizer, there would be no liquid to evaporate out. True; but some liquid plasticizers are still required to make the membrane weldable. Therefore PVC and KEE are classified by two different ASTM numbers. ASTM D4434 and ASTM D6754. ASTM D4434 requires the PVC content to be above 50% of the total polymer amount. KEE sheet is specified by ASTM D6754 that requires KEE to be greater than 50% of the polymer content. Only one manufacturer has a membrane that qualifies for ASTM D6754.