Resin

Any liquid plastic may be called "resin", but in boatbuilding, it generally refers to the primary constituent of a vinylester, or polyester system. It is also used to refer to the mixed result after a hardener has been added, but before it hardens.

Many commercial kayaks are made of polyester resin, as it is the least expensive. Vinylester resins are also used in better quality kayaks.

Some people confuse resins and epoxy. They are very different types of chemicals. Epoxies are rarely used in commercial kayaks due to the cost. However, epoxy is favoured in homebuilt kayaks since it is superior to resins.

If you are repairing a kayak, it is relatively easy to get epoxy to stick to a resin, but difficult to get a resin to stick to epoxy.