In Part One we discussed foam selection, and helped to delineate the differences between Polyurethane foam and EPS foam, as well as the differences between Block-Cut EPS and Superfused (molded) EPS. In Part Two we’ll discuss the various densities (sometimes referred to as “weight”) available for each foam type. As surfboard design and surfing styles have developed, US Blanks has engineered different foam densities to accommodate each need.
“Density” = Pounds-Per-Cubic-Foot of material (foam) for a given space (the blank’s dimensions).
When Gordon Clark and Hobie Alter began producing polyurethane foam surfboard blanks in the mid 50s, they designed their foam for be a similar weight to the wood logs that surfers were accustomed to riding. The heavy foam boards were very sturdy and stable, but difficult to maneuver. As surfer’s skills developed, Clark provided lighter foam, which surfers were able to turn more easily. This trend towards lighter-weight foam continued up until the late 90s, where Kelly Slater, et al., ushered in very thin, narrow, highly-rockered shortboards. These boards allowed for the emergence of aerials, fin-releases, and 360s, but also saw a much greater incidence of board breakage, due partially to the lighter foam, but also the higher impact maneuvers. Since the late 90s, foam density trends have diverged into a wide range of needs. The current “ride anything” ethos requires that shortboards are available in either lightweight or Tow-weight, longboards to be built for high-performance or as throwback logs, as well as any manner of single-fin, kneeboard, asym, funboard, SUP, Gun, and even multi-foam constructions (PU & EPS).
As with any aspect of board building, what you gain in one area, you will lose in another. Lighter weight foam will offer more maneuverability, but inherently less strength. The loss of strength can be mitigated by other construction materials like stronger stringers, carbon fiber, thicker glassing, and stronger resin, etc.
To ensure the exact right foam for any build, US Blanks offers (6) density options for PU blanks, as well as (2) density options for EPS blanks. For PU, the weight is identified by the color on the nose of the blank. Due to a few variables in the manufacturing process (mold compaction, skin-to-core ratio), exact PCF (pounds per cubic foot) for PU foam is not given. Rather, a stock weight (Blue) is designated and then all other densities are referenced from that weight, as a percentage of either more dense or less dense.
From Lightest to Heaviest:
- Orange Density (Competition Weight) is approximately 12% to 13% lighter than Blue. This would be most commonly used for elite level professional shortboards.
- Red Density (Performance Weight) is approximately 6% to 7% lighter than Blue. This is a common selection for a surfer who wants more performance from their shortboard, midlength, or longboard.
- Blue Density (Stock Weight) is the basis for comparison. Blue is the perfect combination of weight to strength ratio; light enough to maneuver, yet strong enough to provide extended use.
- Green Density (Cruiser Weight) is approximately 9% to 10% heavier than Blue. This is a common selection for classic longboard and funboard designs.
- Brown Density (Classic Weight) is approximately 30% to 32% heavier than Blue. This is a common selection for traditional log-style longboards.
- Black Density (Tow-In Weight) is approximately 205% heavier than Blue. This is almost exclusively used in shortboards designed for tow-in surfing.
EPS Blanks (both Block-Cut and Superfused) are available in two densities; 1.5 pcf & 2.0 pcf.
Ultimately, there are some fairly simple standards that you can follow (i.e., shortboards should generally be Orange, Red, or Blue. Longboards should generally be Red, Blue, Green, or Brown). Most performance characteristics in the water will be determined in the shaping bay by contours, rocker, fin setup, etc. but selecting the appropriate foam density is key to having the right foundation upon which to build.
For further information, please reference: http://usblanks.com/blank-options/density-selection/