There is a class of cement board strictly constructed of a Portland cement based core with glass fiber mat reinforcing at both faces. These panels can be immersed in water without any degradation (excluding freeze thaw cycles). These panels do not require the sealing of edges and penetrations to maintain their structural integrity. These Portland cement based products are smaller in size compared with the gypsum core based products. Typically they range in size from to . They are, as one would expect, considerably heavier than the gypsum core type panels.