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.
Urea is a polar molecule that readily / easily dissolves in the polar solvent - water. The term 'organic solvent' is used to describe the more powerful non-polar solvents, sucâ¦h as benzene, or carbon tetrachloride (dry cleaning fluid), that are used to dissolve non-polar compounds.