dioxide, silica sand, kaolin, carbon black and microbeads. [0144] Non-limiting examples of organic fillers that may be used include powders on the basis of polystyrene, polyvinyl chloride, urea formaldehyde resin and polyhydrazodicarbonamide. [0145] Non-limiting examples of short fibers that may be used include, for example, glass fibers about 0.1-1 mm in length and fibers of organic origin, for e