The material is then thermoformed into a hull. After the powder is melted and distributed, a foaming agent is added to the next dump of powdered resin, to create a lighter core of what might best be called expanded polyethylene. A third dump of resin forms a protective skin over the foam. Polyethylene is also used to create durable hulls. Single material and composite-construction canoes are also common.
Hull halves are stretch-formed and riveted to a sturdy keel assembly.
Ribs are then spot-welded to further stiffen the hull. Fiberglass as a construction material is lighter and breaks easier, but can be patched easily. It is both layered on and coated with epoxy and resin or sprayed on with a chopper gun. Many materials and resins are currently being used in fiberglass shops, with an infinite variety in lay-up and philosophy. Frame and skin are also found in folding craft, usually with aluminum frames and synthetic skin, and occasionally appear as ultralight geodesic frames with Dacron or Mylar skins.