The Pentair TLC-24-100 GPD RO Membrane Element is a thin layer composite used in water filtration and purification that provides high quality water from a wide range of water sources. These standard dimension membranes are packaged 100% dry to extend shelf-life of the membrane and to fit common membrane housings. Technically Pentair dry TLC membranes have an infinite shelf life if stored correctly. Great for residential water purification. Pentair also produces commercial grade membranes.