SUP Board Construction
The Foam Core
99% of all standup boards sold today have a foam core. There are a few different types of foam that you can use to make a surfboard/stand up paddleboard.
Over the past few decades polyurethane was the most popular type of foam core for surfboards. Due to its slightly higher cost and its heavier weight per square foot, polyurethane is now infrequently use for large standup paddleboards as they can be prohibitively heavy & expensive. Some other drawbacks are that polyurethane (PU) foam can absorb water & yellow over time and poly is generally deemed as worse for the environment as it contains carcinogens and can’t be recycled. If you are a very competent surfer looking for a smaller performance SUP board then a hand shaped PU core might still be in your future though as its flex & feel are preferred by many top surfers.
Polystyrene now serves as the foam core for most modern standup paddle boards. It is lighter (about 60%), cheaper and more buoyant than polyurethane cores. The downside is that it must be glassed with epoxy resin which is about twice as expensive as polyester resin. There are two main types of polystyrene foams used in SUP boards:
Expanded polystyrene (EPS) foam is the most popular type of polystyrene core. EPS is the same type of foam that is used for things like disposable foam cups and cheap beer coolers. In the past EPS cores could absorb water between the cells if exposed to water. Due to technology enhancements, the highest quality EPS will have fused cells which greatly reduces the ability to absorb water.
Extruded polystyrene XPS is very similar to EPS is typically a little bit more expensive. The extruding process results in a foam that will have less space in between the cells, but can cause delamination issues as gas escapes over time. Advancements in EPS have diminished the advantages of XPS in recent years. The upside to XPS cores is that they can be easier to shape, airbrush and paint.
Stringers are a re-enforcement piece that runs the length of the board and increases its strength. A board can have zero, one or even multiple stringers. Stringers can be made of a lot of different materials such as balsa wood or even PVC plastic (like the pipes in your front lawn).
Balsa Wood Stringer
Fiberglass & Resin
Most boards will have a layer of fiberglass cloth that is coated with a gooey resin that hardens. The weight of the cloth in ounces and the number of sheets of fiberglass influence the strength and the flex of the board. Generally the heavier cloth and more layers of it will result in a more durable board. Often times a board will have more layers of cloth on the top than on the bottom because you will be standing there and putting more pressure on it. All Polystyrene boards (EPS or XPS) use epoxy resin when applying fiberglass.
Glassing a Board
Many EPS/XPS boards may include a vent plug to reduce the chances of delamination that can occur when gas builds up during exposure to heat (out in the sun) or even drastic altitude changes. The downside to these plugs is that if you forget to screw them back in your board will definitely take on some water. Some boards offer newer vent plugs that allow gas to escape without letting water in; thus making them maintenance free.
Goretex Vent Plug
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