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.
SCIP. Solvent vapor annealing on perylene-based organic solar cells. Stefan Grob, Andrew N. Bartynski, Andreas Opitz, Mark Gruber, Florian Grassl, Eduard Meister, Theresa Linderl, Ulrich H rmann, Christopher Lorch, Ellen Moons, Frank Schreiber, Mark E. Thompson and Wolfgang Br tting. J. Mater. Chem.