Wedi building boards have a blue core made from CFC-free extruded polystyrene rigid foam. This makes the Wedi building board an ideal basis for any type of plaster and tile. Wedi building boards can be applied to practically any substrate, serving as waterproof, insulating, versatile, light, and robust material. The blue XPS core is 100% waterproof and remains fully functional even after possible damage. The prefabricated Wedi building board butt joints can be sealed simply using Wedi joint sealant sold separately . The fiber fabric also absorbs tensile forces. All building board systems have great heat insulation properties.