Epoxy is an effective material that is proven in boats ranging from dinghies to ultralight ocean racers and huge motor yachts. It’s more expensive and more difficult to work with than polyurethane
glue since you must carefully measure and mix two components (resin and hardener) before using it. Once you’ve mixed the two you have a very limited amount of time to use it before it begins to harden.
To make the fillets, you have to mix in some very fine sawdust for example. The filler helps to bulk the expensive epoxy and add strength, although the real strength of a fillet comes from the glass tape that lies over it.
Epoxy is also somewhat dangerous to work with. Always use the proper protection as stated on the package. In spite of its drawbacks, however, epoxy is certainly better than polyurethane, from
both a structural and aesthetic point of view. It will produce a stronger, more durable, and better-looking boat than polyurethane.
Some boatbuilders recommend polyester resin as an economical alternative to epoxy as an adhesive in stitch-and-glue boats. Polyester is the plastic from which many “fiberglass” boats are made (the proper name for fiberglass boat construction is glass-reinforced plastic. It is similar to epoxy in that it is a two-part material that requires mixing a resin and a hardener. Although there is plenty of evidence that it works well, it is no longer widely used by home boatbuilders.