Surfboard Foam Blanks Types – Which Is The Best Core?

Surfboards were initially made of hard and heavy woods like Redwood, Cedar, or Wili-Wili. They weighed around 130 to 135 lbs, could get easily damaged, and were particularly difficult to repair. It wasn’t until the 1930s when then surfboard makers started to figure out how to make them lighter.

From combining heavy woods with lighter woods to foam blanks and fiberglass, surfboards have been revolutionized. Nowadays, surfboards are lighter, more buoyant, easier to repair, and a lot easier to maneuver on the wave. What a huge difference, right?

This dissimilarity comes from how surfboards are made now than before, mainly what’s inside the surfboard. In short, what made the modern surfboard improved is what’s inside it – surfboard foam blanks.

Types of Surfboard Foam Blanks

Unlike the wooden surfboards of our ancestors, every modern surfboard utilizes an inner foam core to ensure buoyancy and stability. This core is also responsible for the surfboard to weigh a lot less and becoming more maneuverable.

Surfboard Foam Blanks

Polyurethane (PU)

PU foam is the most popular choice for surfboard shapers. They are used in conjunction with polyester resins to fabricate what is known as polyester or PU surfboard. Take note that there are two different PU foams with somewhat different chemical make-ups to understand.

The first one is the toluene-di-isocyanate (TDI) base, and the other is methylene-di-isocyanate (MDI). TDI is the type of foam blank Clark foam used to make until they closed down. MDI is a fairly new material formulated with less toxic chemicals that have been utilized since Clark’s closure.

PU foam is exceptionally light and easy to shape, and it is one of the reasons most shapers have been utilizing it for so long. Its composition is fine and very stiff, allowing the planer or sandpaper to run over it without tearing chunks off of it but with a few super fine dust only.

This characteristic allows the shaper to sculpt with more detail and to more exact specifications. Most custom-made surfboards are made of PU foam blanks because of this.

Polystyrene (PS)

The PS is another foam core that became a substitute material for surfboard manufacturing when Clark’s closed down. Unfortunately, this material did not follow much because it was difficult to shape and took twice as long to produce the same result.

Although these foam blanks are usually higher in density than PU foam, they are not as strong – which is where epoxy comes in. Another upside of this foam is that it is more environmentally friendly. Most of its waste can actually be recycled.

Expanded Polystyrene (EPS)

The EPS foam core is an alternative foam blank that has gained new supporters since Clark’s closure. This foam blank is also known as the beaded foam and features a closed-cell core. It is derived from the polystyrene foam that didn’t get much following because of how hard it was to shape it.

The EPS foam’s popularity has dramatically grown in recent years. A more environmentally friendly material, it is a lot lighter, which makes it perfect for small-wave surfboards. Surfboard brands like Firewire, and Catch Surf use this type of surfboard foam blank.

You may have encountered EPS at least once in your life. The light disposable coolers you see at the supermarket are EPS foam. You also see them in boxes where they serve as a safety cushion for the items inside.

Extruded Polystyrene Foam (XTR or XPS)

EPS and XPS have often confused many people that thought they are essentially the same. The truth is XPS is very different from EPS.

The XPS is created by mixing PS pellets with chemicals that liquefy them. A blowing agent is then injected into the mixture, resulting in billions of tiny air pockets. Its significant advantage is the closed-cell structure that makes it highly water repellant that if you damage the epoxy covering, you won’t worry about the water getting left inside.

Surfboards nowadays are made with different types of core materials, with each type having its own density, flexibility levels, strengths, and weaknesses.  Below is a reference to some of the most commonly used surfboard foam blanks in terms of density and water resistance.

Core type EPS – S Grade EPS-   M Grade EPS-  H Grade EPS – VH Grade PU normal blank XPS – ND
Density Kg/M3 16 19 24 28 36 32
Water uptake Yes Yes Yes Yes Slightly No
Cell structure Closed^ Closed^ Closed^ Closed^ Closed* Closed
*PU surfboard blanks are a closed-cell structure although, if left open to the elements (not repaired), they will rot in water
^EPS foam is a closed-cell, though if the skin is ruptured, water will fill the air voids in the core

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