A sealant can be applied for purposes of protecting a substrate material from air, gas, dust, liquids, or abrasion. It can be designed to provide thermal and acoustical insulation or serve as a fire barrier. Sealants may have smoothing or gap filling properties, and may be weak or strong, flexible or rigid, and permanent or temporary. They can be applied in joints between materials or over the surface of an entire material. There are natural sealants such as wax, pain, pitch, or tar, and inorganic sealants such as acrylic polymers and silicone polymers. Sealants can be applied to a host of material categories including woods, metals, plastics, textiles, wallcoverings, floorings, and leathers. There are many standards developed by ASTM that govern the type, use, class, and grade of a given sealant.