Polyurethane and Polystyrene foams differ in their chemical makeup. Chemical makeup aside, the three foams that you ask about are different in their cell structure. Both extruded polystyrene foam (XPS) and Polyurethane (PU) foam are a closed cell type foam, which is made up of a suspension of tiny bubbles. Expanded Polystyrene (EPS) foam consists of small beads of polystyrene that have been stuck together. Many are familiar with EPS foam as is commonly used for foam cups and beer coolers. PU foam can be glassed using epoxy resins and polyester resins, whereas XPS and EPS foam can only be glassed with epoxy resins. EPS and XPS resins will react with polyester resins. All foams come in different densities.
FYI - - On a side note, there are two different polyurethane (PU) foams to be on the lookout for, one is a tolulene-di-isocynate (TDI) base, and the other is made using methylene di isocynate (MDI), a less toxic chemical. You should also be aware of a company called XTR, who has a patented system using the XPS foam - its been referred to as a lamination thermo-venting system, where there are holes punched in the deck after the board is laminated. This prevents delamination. The XPS foam has been known to delaminate乧this is due to a problem with the foam degassing under heat and compression. Don't quote me on this one but I haven't seen one person who has made an XPS foam board without a delamination problem. If holes are to be made in the lamination of an XPS - epoxy board, then one must do so with the XTR system if the board is to be sold as a retail product, otherwise the board manufacturer would be violating a national patent. So really, the XTR system is the only way to go with XPS foam. To do an XTR surfboard without violating their patent, one must go through the XTR guys not only for the blank and resin, but also for the glass job (labor). I am not happy with EPS blanks. I as well as others that I know have had problems with the foam collapsing under normal use乧this of course is referring to EPS-epoxy boards that have been constructed in the traditional method of foam core, fiberglass, and laminating resin. There are other methods of construction when referring to EPS-epoxy composites construction. Surftech and the Berger method are two examples of valid surfboard construction methods that involve EPS foam, epoxy resins, as well as other materials and techniques.
FYI - - On a side note, there are two different polyurethane (PU) foams to be on the lookout for, one is a tolulene-di-isocynate (TDI) base, and the other is made using methylene di isocynate (MDI), a less toxic chemical. You should also be aware of a company called XTR, who has a patented system using the XPS foam - its been referred to as a lamination thermo-venting system, where there are holes punched in the deck after the board is laminated. This prevents delamination. The XPS foam has been known to delaminate乧this is due to a problem with the foam degassing under heat and compression. Don't quote me on this one but I haven't seen one person who has made an XPS foam board without a delamination problem. If holes are to be made in the lamination of an XPS - epoxy board, then one must do so with the XTR system if the board is to be sold as a retail product, otherwise the board manufacturer would be violating a national patent. So really, the XTR system is the only way to go with XPS foam. To do an XTR surfboard without violating their patent, one must go through the XTR guys not only for the blank and resin, but also for the glass job (labor). I am not happy with EPS blanks. I as well as others that I know have had problems with the foam collapsing under normal use乧this of course is referring to EPS-epoxy boards that have been constructed in the traditional method of foam core, fiberglass, and laminating resin. There are other methods of construction when referring to EPS-epoxy composites construction. Surftech and the Berger method are two examples of valid surfboard construction methods that involve EPS foam, epoxy resins, as well as other materials and techniques.
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