PU vs. EPS Epoxy vs. Carbon Fiber Surfboards: What's the Difference?

Introduction

There’s still some confusion around the names and types of materials used in surfboards today, so in this introduction, we’ll clarify the common combinations of foam blanks and resin used in modern surfboards.

Surfboards with PU (polyurethane) blanks are laminated using polyester resin.

Surfboards with EPS (expanded polystyrene) blanks are laminated using epoxy resin.

PU Foam (polyurethane)

Polyurethane surfboards are the most popular and widely used today, including among elite surfers on the CT (Championship Tour). Their construction is generally a bit heavier and less durable than epoxy boards, but they tend to feel more consistent and predictable underfoot. This is due to their slower flex pattern and denser foam compared to epoxy constructions, which results in fewer “surprises” and more control during surfing—especially during harder turns or quicker maneuvers.

Polyurethane also absorbs less water when dinged and is less prone to heat damage than epoxy.

EPS Foam (Expanded Polystyrene)

The term “epoxy board” refers to the use of epoxy resin in the lamination process. These boards are built using EPS (Expanded Polystyrene) foam blanks, which are only compatible with epoxy resin. Compared to PU/polyester constructions, EPS/epoxy boards are generally lighter and stronger.

They also tend to feel more lively and flexible underfoot due to their faster flex pattern and lower foam density. This added liveliness, while beneficial in certain conditions, can feel less predictable or consistent than PU, especially in high-performance situations that demand precision and control.

In fast, powerful waves, the lightweight nature of EPS boards may cause the rider to feel surface imperfections (or “bumps”) on the wave more directly through the board — particularly in the legs — since the board doesn’t cut through chop as well as a heavier PU board.

On the other hand, that same lightweight construction offers excellent speed, agility, and responsiveness in weaker or slower waves, where liveliness becomes an advantage.

EPS foam also tends to be more resistant to pressure dents under the surfer’s feet when compared to PU, especially in higher-density blanks. However, EPS is more sensitive to heat, particularly if left inside a hot car during the summer or exposed to direct sunlight for long periods.

For an all-around construction with a good weight-to-strength ratio, we prefer to work with 2.0 lb/ft³ EPS density.

Surfboard Flex Concept

Surfboard flex shares similar principles to fin flex: Flex = projection, which refers to the speed generated when coming out of a bottom turn or carrying good speed into a top turn. This projection occurs when the board twists or flexes into the shape of the wave, depending on the force applied to it, and then snaps back into its original shape. During this process, it builds up and releases energy, resulting in forward projection down the line.

How do we control surfboard flex? Ever since PU (polyurethane) blanks became the standard in surfboard construction, wooden stringers have been used to add strength and stiffness. A board with a center stringer helps create a pleasant feel and stiffness right under your feet, which is crucial since most of the force applied to the board by your foot is absorbed by the center. However, this central stringer placement leaves the rails softer, which can result in a different type of flex, twist, and wobble, leading to a slight loss of speed.

Stringerless Boards In recent years, shapers have begun testing new materials and utilizing stringerless EPS and XPS blanks. A widely adopted concept is using carbon tape down the center of the board, creating an effect similar to the wooden stringer in PU blanks. This carbon tape offers excellent strength and stiffness while being lighter than a wooden stringer, making it a fresh alternative in surfboard construction alongside traditional PU boards.

EPS Blanks with and without a Stringer

As mentioned earlier, the stringer is the wooden line running down the center of the board, responsible for adding strength and stiffness. All PU boards come with a stringer, but EPS blanks give you the option to have one or go stringerless. If you choose a stringerless blank, carbon fiber tape must be added to compensate for the lack of strength and stiffness. A stringerless board is lighter (due to the absence of the wooden stringer) and offers more flex compared to one with a stringer. However, to prevent the board from becoming overly flexible (which is not ideal), this carbon tape is added to provide stiffness in strategic areas of the board.

With this in mind, we utilize three construction methods widely popular internationally for stringerless Epoxy boards: Full Carbon, Slingshot Carbon, and Stringerless Carbon.

Full Carbon Vacuum Tech

We build surfboards entirely with carbon fiber and XPS foam, using advanced lamination techniques to maximize performance and durability. Our process employs a vacuum bag system to apply maximum, evenly distributed pressure during lamination, ensuring a superior and consistent bond between materials for a stronger, lighter construction.

This type of construction is significantly stronger than traditional fiberglass boards, thanks to the superior properties of carbon fiber. Unlike conventional fiberglass cloth, carbon fiber responds more quickly and offers elastic rebound.

The result is noticeable energy release during bottom turns and powerful maneuvers—areas where the board typically flexes and stores energy—translating into added speed and drive.

For lighter boards, we recommend using XPS foam with a density around 2.0 lb/ft³. For increased durability and resistance to pressure dents, especially under the surfer’s feet, a higher-density foam such as 2.3 lb/ft³ is ideal.

Slingshot Carbon

Very similar to Stringerless Carbon, except the carbon tape does not extend all the way to the end of the tail. This causes the board’s tension and flex strength to build up where the carbon is present and release at the very tip of the tail, which offers greater flex due to the absence of carbon.

Stringerless Carbon

This construction adds carbon fiber where the stringer would normally be, thereby simulating its presence. This option is recommended for those who want to maintain the feel of having a stringer in their board and can be applied to all models, regardless of whether the waves are small or large.