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.
It's in the name. Urethanes are a type of chemical formulation, as are. acrylics. So, basically, polycrylic is a formulation that uses a. different chemical substrate of plastics than polyurethane does. These. different substrates create a variety of hardnesses, moisture resistance, opacity, and durability.