Porcelain tiles are composed of fine porcelain clay and fired at a much higher temperature than traditional ceramic tiles making them much harder and more dense. Due its highly durable make-up, porcelain is more resistant to scratches and can withstand extremes of temperature. It is very stain resistant, has a very low water absorption rate and so can be used for interior and exterior applications. Porcelain tiles can be either glazed or unglazed. Unglazed porcelain tiles are usually polished to a high gloss shine but because they are not coated with a glaze, such tiles benefit from the application of a penetrating sealer to give it added stain resistance and to aid cleaning.