 Made from materials such as polymer concrete, fiberglass, structural plastic and steel, liner systems are the channel and grate components that are assembled in the trench and around which concrete is poured to form a drain system.By themselves, these liner systems do not have the strength and integrity to hold up under the physical requirements needed for the drain.A concrete (or asphalt) drain body is required to encase the channel to give the channel compressive strength and rigidity to ensure the drain will be able to withstand the traffic load it was designed to handle.