What’s in a blank?


Surfboards utilize what is known as “sandwiched” construction. They are constructed of two or more layers of materials. The typical contemporary surfboard has a foam and/or wooden “core”, with a fiberglass “skin”. Most surfers are aware of the different skin materials, e.g. E-cloth, S-cloth and Volan cloth, with their associated resins; polyester or epoxy. But few know the details of the materials that make up the core.

There are three basic core materials used in contemporary surfboards: (1) wood (usually balsa, but sometimes redwood, basswood or agave wood), was the original core material, polyurethane foam (PU) replaced balsa and has been the standard for the last 50yr, and expanded polystyrene foam (EPS), which has been gaining popularity over the past 10 yr.

When talking about the characteristics of core materials, “density” is usually always mentioned.  Density is defined as the amount of mass in a specified space. The denser an object is, the less likely it is to float. But, higher density materials are also less susceptible to compression dings. Below are the densities of the most common wood core materials:


Balsa 8.00
Bass 20.00
Cedar 23.00
Redwood 28.00


US Blanks manufactures surfboard blanks in a variety of densities (see table below).


Orange 1.96
Red 2.09
Blue 2.25
Green 2.48
Brown 2.95
Black 4.61


EPS foam is manufactured in several different densities, including;





A big advantage offered by EPS foam is its superior buoyancy over all other core materials. EPS is manufactured by expanding spherical beads in a mold, using heat and pressure to fuse the beads together. Each bead contains hundreds of mini air bubbles. It is this trapped air that accounts for it superior buoyancy. But there’s a catch…EPS foam will readily absorb water if the fiberglass shell is ruptured. The lower the density, the more open space exists between the beads and the more readily it will absorb water.

When considering a custom board, keep in mind your performance requirements. If lightweight is a priority, consider asking for Orange or Red density PU, or EPS. If durability is a priority, ask for greater blank density such as Red or Blue PU, or 2.0PCF EPS. Use a less dense core if you need a lot of buoyancy but want to minimize board volume. Surfers who enjoy the momentum offered by greater mass might consider Green density PU foam for their traditional log. Another thing to consider is cost. EPS foam is not compatible with polyester resin, and the more expensive epoxy resin must be used exclusively. Likewise, EPS blanks are more expensive than PU blanks. Expect to pay a $90-$100 premium for an EPS/Epoxy surfboard.

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