Laboratory testing was conducted to develop chemical resistance data using immersion tests. Six FML materials (polyvinylchloride, chlorinated polyethylene, chlorosulfonated polyethylene, high density polyethylene, epichlorohydrin and ethylene propylene diene terpolymer) were tested. Twenty chemical solutions providing a range of chemical challengers; acid and base, polar and non-polar, organic and inorganic, and increasing chemical concentration, were used. Duration of immersion were 1, 7, 14, 28, and 56 days, and four month increments for up to two years. All immersion tests were conducted at two temperatures, 23À and 50ÀC. Liners were evaluated for changes in appearance, weight, dimensions, and tensile properties. Procedures and criteria for evaluating immersion test results were developed using data from this study and comparing these data with comparable data from other studies, published reports and criteria, and liner manufacturer recommendations. The criteria for chemical resistance included the need for a liner response to have stabilized, retention of minimum physical properties, and maximum percent change of physical properties. A mathematical curve fitting method is propsed for evaluating immersion data as a function of time. The method assumes the liner approaches a limit of physical property change (stability) asymptotically. The method can be used to predict the ultimate end point of physical property change and sampling time intervals for continued immersion testing.