a polymer - based composite structural board for in - ground and above - ground use without material degradation has a polymer material or predominantly polymer material core layer with a density between 1 . 6 lbs / ft 3 and 25 lbs / ft 3 . a facer overlays , is generally coextensive with , and is bonded to at least one of the major surfaces and preferably both of the major surfaces of the core layer . the facer enhance the integrity and fastener pull through strength of the polymer - based composite structural board as well as other desired physical and performance characteristics of the polymer based composite structural board . the polymer - based composite board is used in foundation wall systems , utility conduit systems and other systems where the composite board is in ground contact .