All surfboards utilise an inner foam core in order to ensure the end product has sufficient buoyancy. Foam cores are shaped and refined from a foam blank and made of two foam types:
Today, the most common forms of foam are Polystyrene: Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS). These foam blanks are blown from a mould and then shaped or refined by a shaper.
SO WHAT ARE POLYURETHANE OR POLYSTYRENE BLANKS?
The blanks are made by firstly mixing two chemicals (polyol and diisocyanate) to form a long-chain molecule called urethane. This is then transferred through a pipe, and at the same time, blasted with carbon-dioxide. This makes the foam expand so it is then compressed and passed through a heat chamber to release any tiny gas bubbles. This causes it to expand, burst, leaving a spongy substance to shape.
Expanded Polystyrene (EPS)
You are probably already familiar with EPS foam (in drink coolers). This foam blank is made up of small expandable foam balls that inflate when heated (to make it expand to form a low-density mould). When the foam balls expand, they trap air meaning these blanks usually consists of 96-98% air and 2-4 % polystyrene. This makes it one of the lightest out of the three types of foam blanks. However, it is not water resistant like XPS.
Extruded Polystyrene (XPS)
This type is manufactured in a unique continuous extrusion way. The blanks are made by firstly mixing special chemicals with polystyrene crystals. This chemical liquefies the polystyrene. Next, a blowing agent is applied to create tiny little air pockets. This mixture is put in to an extruder where the mixture melts under controlled heat temperatures and pressure, forming a liquid. The liquid is then forced continuously through a die where it expands to foam that you can shape. The end result is a unique closed-cell foam blank (water repellent).
|Polyurethane||Higher density, improved flex pattern and increased heat resistance||Compresses easier|
|Polystyrene||Lightweight, improved buoyancy, higher compression resistance and stronger||
Lower resistance to heat
Surfboards are typically constructed with a stringer running down the centre of the board. The stringer acts as the back bone or spine of the surfboard providing extra strength and rigidity. Stringers can be made from wood types such as (bamboo, balsa, paulownia or ply) or PVC (polyvinyl chloride).
Traditionally, there will only be one stringer in a surfboard however there can be more. Multiple stringers (2 or more) are usually incorporated when you need to minimise flex and wobble. You can usually see this design in Longboards.
Foam on its own is too weak to surf. So, to give it strength fiberglass cloth is added. This is applied as a layer (or two or three) to the entire length and width of the surfboard, both top and bottom. 2oz, 4oz and 6oz cloth are your typical weighted cloths that can be applied. In addition to fiberglass cloth, you can use other materials to strengthen a surfboard, such as Kevlar, carbon fiber or natural materials like bamboo or hemp.
Resin is used to bond the cloth to the foam blank. Resin is poured straight onto the cloth and the board until the cloth is completely saturated. There are two common types of resin: Polyester resin and Epoxy resin. Both of these resins may be used with polyurethane foam, but only epoxy may be used with polystyrene foam.
Polyester Resin / Fiberglass
These two materials are used with polyurethane (PU) foam blanks. The benefits of Polyester resin/fiberglass include that it is cost effective. However a disadvantage is that Polyester is much more susceptible to cracks and dings.
Epoxy Resin / Fiberglass
Extruded Polystyrene (XPS) and Expanded Polystyrene (EPS) blanks are quite popular. However, these materials will break down and dissolve if polyester resin is applied. That means only epoxy resin can be used. The benefits of Epoxy Resin/Fiberglass include that it is lighter (so therefore more buoyant) and typically stronger. Unlike Polyester Resin, Epoxy is more resistant to cracks and dings. However, a disadvantage is that it is more expensive.
OTHER STRENGTHENING MATERIALS
Bamboo is extremely popular today, especially on SUPs due to its unidirectional and bilateral strength properties. Apart from proving additional strength, a great benefit is that it is an environmentally friendly material to use. Since Bamboo is light and durable, it also offers greater resistance to dings.
Using carbon fiber in the manufacturing process offers a very strong and ding resistant surfboard. This means the life expectancy of your board will be greatly extended by the addition of this fiber.