The Case for Polyurethane

By Ned McMahon

The past few months have been an interesting roller coaster ride from the panic of lack to an over abundance in the surfboard blank world. The door of opportunity has been thrown wide open to many new types of manufacturing methods and materials. Some materials have been on the fringes of the surf world for years, while other new ideas finally had a space to surface.

Considering all these material alternatives is an important process toward ensuring we have the best materials to make our beloved surfboards. “The Best”, of course, has many components – strength, durability, environmental impact, aesthetics, ease of production, and cost. Now that many alternative methods have been investigated, once again polyurethane foam blanks are rising to the top.

We (all surfers) owe a debt of gratitude to Mr. Clark. For over 40 years he has given us a good quality, durable material that was easy to work with, customize with color, and affordable. Clark’s continued advances in his product quality and variety (with the help of close tolerance blank plugs from Rusty) have allowed many to become shapers that may have never even attempted mowing foam with plugs and densities from the beginning years.

Even though Clark shut down, he continued to develop his product to the end. He was working on new formulations and was actively looking for the next product or tool to make his operation even better. Now, it’s a new day with many choices of materials to build surfboards. Some materials and methods such as the hollow carbon and parabolic wood railed surfboards are great technology and produce great products and they aren’t practical for large production runs nor do they allow for the ultimate customization that many surfers have become accustomed to.

EPS or polystyrene has made some big inroads to the market now as well. To some, EPS looks to be the best alternative to polyurethane. Polystyrene is a material that was developed as a result of the war effort of the ‘40s and has been is use since then. When Clark was originally starting his blank production, he had the opportunity to use polystyrene too so why did he choose polyurethane back then?

Polystyrene is either extruded or expanded from bead. The extruded foam comes in big blocks that need to be re-cut (hotwired) into a blank form prior to a stringer being glued in. The expanded polystyrene is also expanded into a mold usually in block form too. Today molds have been made into a shape like a regular blank that the foam expands into. Since the molds are metal, they are very expensive and difficult to make. The material is also more difficult to shape cleanly.


Polystyrene does have some advantages. One advantage is the foam can be made in very light densities. Another is that the polystyrene maintains good strength because the foam remains a constant density throughout its thickness. Some surfers also like the feeling of extra buoyancy a polystyrene board offers.

Polystyrene has its disadvantages too. Polystyrene boards are most often glassed in opaque finishes because the foam doesn’t finish in the shaping process very cleanly. Normally the foam must be sealed before it is glassed and it must be glassed with epoxy resins. Workers exposed to epoxies are more likely to have adverse reactions to the resin than with the polyester resin used with polyurethanes. The foam can be more difficult to shape. While surfers find the buoyancy good, the stiffness is something that doesn’t feel as good.

So this brings us back to polyurethane. Polyurethane foam is expanded in molds that are less expensive and easily made therefore allowing for many more choices in blank size and shape. The foam is relatively inexpensive. The foam takes colors and paints well therefore infinite customization is possible from the shaping to the finish. The foam finishes very nicely when it is produced correctly. Production problems range from air bubbles in the foam, pour marks due to uneven distribution of the foam in the mold, varying density and soft spots from improperly measured volume and placement in the mold, and softer areas toward the center of the blank.

TDI Polyurethane is environmentally on the way out. The “T” is for toluene and its use is slowly becoming banned from the US. Some manufacturers are still allowed use it through grandfather clauses and expensive factory retrofits. Workers must also be well protected when working with toluene. Environmental concerns are ever present and on the rise with surfers becoming increasingly interested in environmental issues on all fronts. Yet several TDI blank plants have set up just south of the California border for cheap labor and, more importantly, to get around any EPA issues in the US.

Thousands of blanks have arrived into the US from plants around the world - South Africa, Brazil, Argentina, Spain, Australia, China, and the UK. The vast majority of these manufacturers use the TDI process. In addition to the TDI, the viability of shipping a lightweight product like foam in containers around the world just doesn’t make sense. Supply by shipping container around the planet is hardly green thinking. Shipping of just the raw materials needed to make foam is at least 18 times more fuel efficient than shipping blanks.

There is another polyurethane now available and it is something that even Clark was working on before he called it quits. This polyurethane is a foam system based on MDI (methylene di-phenyl di-isocyanate) rather than TDI. The main health hazard associated with isocyanates is inhalation of aerosols which can cause respiratory problems. When blowing rigid foams such as surfboard blanks, there is an additional hazard of partially cured foam dust from the de-molding process. MDI is by far the least hazardous of the commonly available isocyanates since its vapor pressure is some 2500 times less than that of TDI at ambient temperatures.

Modern MDI blank plants, such as Homeblown US in San Diego, rely on a computer controlled pouring machine that ensures the foam is delivered precisely in the right amounts to each part of the mold. The result has an astonishing consistency in production with minimal waste. The air voids and pour marks are eliminated and there is a consistent density and hardness through the entire thickness of the blank. All this adds to MDI foam being 15-25% stronger in compression than any other TDI foam of the same density.

Finally, we are back to where we started (but not quite). Mr. Clark knew back in 1960 what a fantastic material polyurethane foam was for the manufacturing of surfboards. He had the opportunity throughout his over 40 years in business to experiment with different materials and polyurethane still won out. Polyurethane is easy to work with, takes color beautifully for infinite customization, is strong, flexible, and relatively inexpensive and it remains the best surfboard system today.

The one thing about polyurethane is the choice of TDI vs. MDI. All the TDI companies of the world - at their best – can only hope to achieve what Clark left behind. Clark knew that MDI was the future of polyurethane, and polyurethane is still the future of surfing.