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.
Other organic solvents that are used in extractions include ethyl acetate (CH3CO2C2H5), methylene chloride (CH2Cl2), chloroform (CHCl3), hexane (CH3(CH2)4CH3), and benzene (C6H6). Benzene and chloroform are usually avoided as solvents due to their carcinogenic nature.