A CTA (Cellulose Triacetate) membrane is a paper by-product membrane bonded to a synthetic layer. Due to its cellulose composition, a CTA membrane requires chlorine in the water source to keep bacteria from forming on it. A CTA membrane has a rejection rate of between 85-94%. CTA membranes have an average life expectancy of 18-24 months and are considered inferior to TFM membranes. Premier only uses TFM (Thin Film Membrane) membranes, which are made of a synthetic material. A TFM membrane requires the chlorine be removed prior to the water entering the membrane. A TFM membrane has a rejection percentage between 95-98%, which is much higher than the CTA membrane. A TFM membrane will last between 2-5 years. Many hospitals use TFM membranes in their hemo-dialysis (kidney) machines because of the higher purity water they produce.