You can choose among several classes of topcoats when you need to protect a surface such as a floor. Two popular types of topcoats are those made from epoxy and those made from aliphatic urethanes. The epoxy topcoat will give good results in a range of applications, but aliphatic urethanes display superior performance, including resistance to abrasion, chemicals and UV light. They are environmentally friendly and emit little odor. These characteristics stem from the primary ingredient in aliphatic urethane: hexamethylene diisocyanate (HDI) and its homopolymer.