Epoxy and polyurethanes are both thermosetting polymer resins. Therefore, they cannot revert to their pre-catalyzed state nor will they melt if heated. It is also worth nothing that these resins are from different chemical families. This article will highlight the differences between epoxy and polyurethane.
Epoxy
An epoxy resin, once cured, offers a hard and resistant plastic material. It does not offer much versatility in its shape, but it will offer greater resistance to the elements found on sites such as water and moisture. Epoxy hardening is relatively predictable since it is linear and constant.
Finally, epoxy, due to their chemical composition, tends to yellow in the presence of UV rays. It is therefore recommended to use it in industrial settings, to create coatings that are resistant to impacts and offer better durability.
Polyurethane
Polyurethane resins can be found in different forms: coatings, elastomers, foams, transparent varnishes, etc. Since they are reactive to many other chemical elements, they can be used in a variety of ways. For example, a polyurethane resin mixed with water will form a cushioned foam. However, since they are more reactive, they are also less forgiving than epoxy resins in harsher environments where contaminants (e.g. moisture) may be present during installation.
Polyurethanes will also offer good resistance to ambient temperature changes and thermal shock. They are therefore the preferred solution for outdoor applications. Also, aliphatic polyurethanes will offer increased resistance to yellowing and discoloration caused by UV rays. Since they are less durable, they are often used in combination with epoxy to optimize systems, taking advantage of the durability of epoxy and the better aesthetic performance of polyurethane.