Bicast, or PU, leather is a material composed of split leather coated in a layer of polyurethane embossed with patterns to resemble the grain of higher-quality leather.
The polyurethane coating is added to visually and texturally improve split leather for sale. The glossy result more closely resembles the look and feel of top-grain leather, though with great differences to even casual observation. As the split serves only as a backing for this layer of plastic, many of the qualities of leather are lost, including durability and the development of greater suppleness and patina over time.
The highest-quality leather goods are traditionally made from full-grain leather, hides left as untouched as possible to preserve natural characteristics, or more pliable top-grain leather, hides that have had been processed to have their surface imperfections removed. In either case, the thin surface layer of hide is separated for use from the thick inner layer. The inner layer, called split leather, is therefore a by-product of manufacturing process. Split leather is more abundant on the rawhide than top grain and is stiffer and more prone to cracking over time. It is also less marked with idiosyncrasies and imperfections, as it lies beneath the outer layer of skin. As a result, it is less expensive to the manufacturer and to the end-consumer.