Rapid Prototyping involved creating a working model of various parts of the system at a very early stage, after a relatively short investigation. The method used in building it is usually quite informal, the most important factor being the speed with which the model is provided.
There are water-and solvent-based -- also called oil-based -- polyurethane varnishes. Water-based polyurethanes are more environmentally friendly and safer to use than solvent-based, but they are not as resistant to wear and tear as solvent-based products.
A polyurethane coating (or urethane floor coating), is a highly flexible, highly abrasion-resistant floor coating that is known for its shine and longevity. Developed in 1937 by I.G. Farbin, these materials were used to create gum rubbers, rigid foam, and elastomers.