When surfing first became popular as a sport 50 odd years ago, surfboards were made out of wood. These surfboards were extremely heavy, easily damaged, and difficult to repair. The surfboards of today are much lighter, float better, are easier to repair, and are capable of great maneuvers on the wave. What's made the huge difference?
Nowadays, the majority of surfboards are made with a foam middle, and then coated with a foam appropriate polyester or epoxy resin.
The foam in the middle of your surfboard does several things. First, it contributes to the board weighing a lot less. Secondly it enables the board to float better (also known as buoyancy). There are a couple of different types of foam that can be used for making surfboards. Either way, these foam inners are known as surfboard blanks. Surfboard blanks are available in a huge range of lengths, thickness and widths.
When selecting a surfboard blank it is a wise idea to choose one that is a bit bigger than the surfboard you are wanting. An inch or two extra in width, and up to no more than 6 inches in length will give the surfboard shaper enough to work with. So when checking out the surfboard blanks be sure you are pretty definite on the finished product.
Surfboard blanks can either be shaped by hand or with machines. The type of foam you select in your surfboard blank will determine whether the final product will be an epoxy surfboard or traditional fiberglass.
Epoxy surfboards are constructed using EPS or expanded polystyrene. (This is the sort of foam that your beer cooler is made from but a lot more dense.) EPS foam blanks require an epoxy resin as the polyester resins destroy the EPS foam.
A traditional fiberglass board has a polyurethane foam core. The foam blank is shaped and then covered with fiberglass and then lastly the polyester resin laminate. Fiberglass surfboards have been around since the 1960's, superseding the wooden surfboard.
Polyurethane foam is the foam most of us think of when we hear the words "Clark foam". So basically, surfboard foam blanks are made from either EPS or polyurethane foam. This in turn determines the sort of resin that will be used in making the surfboard. Epoxy surfboards have EPS cores. Polyurethane blanks are compatible with polyester resins and traditional fiberglass surfboards.