One of the most common and versatile is the foam pig which is cut or poured out of open cell polyurethane foam into the shape of a bullet and is driven through pipelines for many reasons such as to prove the inner diameter of, clean, de-water, or dry out the line. There are several types of pigs for cleaning in various densities from 2 lb to 10 lb foam and in special applications up to 20 lb. Some have tungsten studs or abrasive wire mesh on the outside to cut rust, scale, or paraffin wax deposits off the inside of the pipe. Other types are fully or criss-cross coated in urethane, or there are bare polyurethane foam pigs with a urethane coating just on the rear to seal and assist in driving the pig. There are also fully molded urethane pigs used for liquid removal or batching several different products in one line.