Are you ready for some schooling? We’re going to be talking about two different types of foam that are commonly incorrectly identified. Wakesurfing in particular is filled with folks that talk really confidently and LOUD, but don’t know squat. Such is true in all segments of society, talk with confidence and at least some folks will believe your spiel.
Here is a picture and without doing any reserach, what would you call these cups?
Styrofoam cups, right? NOPE! That is NOT Styrofoam. It has a similar chemical makeup to styrofoam, but that white pellet foam is actually expanded polystyrene and Styrofoam is an extruded polystyrene foam. Styrofoam is actually a trade name of that extruded polystyrene foam manufactured by Dow Chemical. Expanded polystyrene is commonly called EPS foam and extruded polystyrene is commonly called XPS foam.
Here is a picture of some XPS foam manufactured by Ownes Corning under the trade name Foamular.
The Dow Chemical XPS is a blue color and the Owens Corning XPS is this Pink color. Both foams are the same chemical makeup.
XPS foam is made through a ridiculously complex process called polymerization. One of the chemicals used in that process is polyethelene and if you’ve followed us for any length of time, you know that NOTHING, but NOTHING sticks to that stuff. We use it as wet out table covering and we can peel off the cured epoxy and reuse the plastic sheet, if need be.
XPS foam starts as a clear molten fluid mass. That is what our plastic knifes and forks are made from, even SPORKS! XPS foam goes through a separate process of extrusion, where the molten polystrene is squeezed through a slot to form flat sheets and allowed to expand in the foam board you see in the pictures in this article.
It is a true closed cell foam, it starts as a liquid, a molten liquid, but still a liquid and then when it cools it forms a solid again. The point being that it’s a single chemical compound unit, that changes it’s state during the manufacturing process. Contrast this to Expanded Polystyrene Foam, or EPS, which is individual beads of foam sort of squished together to form a foam board. EPS, then is not a closed cell foam, however the current stated of manufacturing makes surfboard specific EPS foam almost impervious to water. “Almost” being the key part of that phrase.
Here is a picture of a 4′ x 8′ sheet of XPS foam.
It is commonly used in thermal insulation, because it has poor heat transfer capabilities. The reason is that XPS foam is about 90% air!!!! Virtually all foams have an expansion process during their manfacture that is caused by expanded gases, either a blowing agent or trapped air.
XPS is typically about 1.8 pound density and has great compressive strength.
Why wouldn’t we use this as the core of a wakesurfer? There are folks that use it for a core in some surfboards, in fact there is a brand XTR, that is in fact an XPS foam. The process of making a surfboard with it is pretty complicated and requires small pinholes to allow trapped gases to escape. In a secondary bonding phase, the surface must be sort of gouged to allow excess resin to grab into the depressions. The reason being that copolymerization with polyethelene, which NOTHING sticks to.
We’re going to use the XPS as a deck side component for our multi-density foam composite sandwich core test board. We are looking for the right combination of stiffness, compressive strength and low weight, all wrapped up into one! It’s not as tasty as surf style front shuv, but it’s still fun.
So now you’ll never ask for a styrofoam cup again, right? 
We don’t expect that, but at least you’ll understand the correct terminology and be able to properly identify when someone doesn’t quite know what they are talking about!
Thanks so much for following along.
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