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.
Quick Answer. Colloquially, people use the term urethane to refer to a type of varnish, while the term Varathane refers to a brand of varnishes, sealers and similar products. Technically, urethane is not the correct term for the wood-sealing product, even though it is commonly used.