What are the primary differences between oil-based and waterbased polyurethane?
Greg Williams: Enough difference to consider them very different finishes. The oil types are more like traditional varnish. They darken over time, dry much more slowly, require attention to recoat intervals, and have much more objectionable odors. Both the coating and the cleanup solvents may be flammable. The waterbornes typically (there are many differences between brands and types) are fast drying, with low odor, are nonflammable and more quickly recoatable.
Michael Dresdner: To take it a step further, most waterbased polyurethanes go on clear and stay clear indefinitely, while oil-based ones go on amber and continue to darken over time. As for durability, oil-based polyurethane is typically more chemical resistant and more heat resistant than waterbased.