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.
Restoration Shop UB Urethane Basecoat, AL Acrylic Lacquer, PPG DBC Basecoat & DDL Acrylic Lacquer and related solvents are not compliant. for purchase in the State of California and may contain VOC which exceeds the limits in other districts/states.