Below are some foam specifications for XPS available in the U.S.
psi = pounds per square inch (compressive strength)
pcf = pounds per cubic foot (density)
Dow "Blue Foam" (XPS):
STYROFOAM™ High Load 100 -- 100 psi min. compressive strength (density, 3.0 pcf)
STYROFOAM™ High Load 60 = 60 psi min. compressive strength (density, 2.2 pcf)
STYROFOAM™ High Load 40 -- 40 psi min. compressive strength (density, 1.8 pcf)
STYROFOAM™ Brand Square Edge Insulation -- 25 psi (density, 1.6 pcf)
STYROFOAM™ Brand Square Edge Insulation (U.S. Only)
STYROFOAM™ Brand Residential Sheathing (RS) -- 15 psi (1.3 pcf)
Dow Blue Foam Densities (Dow Building & Construction Answer Center)
Owens-Corning "Pink Foam" (XPS also):
Foamular 1000 -- 100 psi, 3.0 pcf density
Foamular 600 -- 60 psi, 2.2 pcf density
Foamular 400 -- 40 psi, 1.8 pcf density
Foamular 250 -- 25 psi, 1.55 pcf density
Foamular 150 -- 15 psi, 1.3 pcf
XPS & EPS Foams
Dow Blue Foam ("Styrofoam") and Owens-Corning Pink Foam (Foamular) are extruded polystyrene (XPS). XPS is a closed-cell polystyrene foam that is not porous (made light by injecting a blowing agent during polystyrene extrusion, that causes small bubbles to form in the polystyrene as it comes out of the extrusion die) and therefore does not absorb water. Resin does not adhere well because the foam is not porous (less surface area for bonding because there are no connecting passages, open spaces, between cells) and some gas is released from the cells when they are ruptured. Some surfboard builders claim good success glassing XPS after the shaped core (final) is scored/roughed with 20-50 grit sandpaper.
EPS foam is expanded polystyrene. EPS is made by heat fusing polystyrene beads. There are air spaces between beads, which means it will soak up water, but epoxy resin bonds well to it in the 2.0-2.5 pcf densities. It can be found in 1.0-3.0 pcf densities. The 2.0-2.5 pcf densities are often used for surfboard cores -- vacuum veneer sandwich technologies have been used for EPS densities less than 2.0 pcf.
Foam Skateboard Press Requirements
Based on numerous posts/threads at silverfishlongboarding.com as well as information at roarockit.com, you want a foam with a minimum compressive strength no less than 15 psi for skateboard presses/molds. This is because atmospheric pressure is 14.7 psi (for vacuum pressing).
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What is EPS Foam?
The information below can be found at the following link. It is a good brief discussion about EPS and XPS foams:
E.P.S. stands for Expanded Poly Styrene and is a lightweight product that is produced by expansion of small solid plastic particles of polystyrene. The plastic polystyrene expansion is achieved by the virtue of small amounts of pentane gas dissolved into the polystyrene base material during its production. Butane gas or propane gas can also be used as a blowing agent, however the Pentax gas is most environmentally friendly.
The gas that has been introduced expands under the action of heat that is applied in the form of steam which then forms the polystyrene particles into perfectly closed cells of EPS. The beads are sorted by weight and size and allowed to age for a given period before proceeding on to the next stage of production. The EPS closed cell beads are then molded into various forms suited to their application. This process has now transformed the beads which now occupy approxmately 40 times the volume of the original polystyrene granule.
The manufacturing of EPS foam process takes several steps in order to produce the materials and products we have all come to know.
The polystyrene particle granules are pre-expanded by free exposure to steam which produces closed cell non-interconnecting beads.
After the pre-expansion, the beads still contain small quantities of both condensed steam and pentane gas and are allowed to cool in large silos where the air gradually diffuses into the pores, replacing in part the two expansion components of steam and pentane gas
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The beads are allowed to age and go through this diffusing process after which the beads are moulded to form blocks or customized formed products. The mould serves to shape and retain the beads in a pre-form shape and then steam is once again applied to promote additional expansion. During this application of the steam and pressure causes the fusion of each bead to its neighboring beads, resulting in a homogenous end product.
Once the product is allowed to cool for a short time, the product is removed from the mould for further conditioning or cut into various shaped by use of hot wire devices or other appropriate techniques.
Regrind
Some foam manufacturers will use recycled or ground up foam material mixed with their virgin foam which is a great way to recycle the material. While environmentally a very sound process to produce some products, the end product will not have the same structural integrity.
Porosity of EPS Foam
EPS foam by its nature is mostly air, and depending on the density of the foam, there will be more or less air between the fused closed cell beads of EPS. The higher the density, the more beads and consequently the less space for air between the beads.
There is some confusion between water absorption with EPS foam and fusion of the beads. Because of the porosity of the foam, the water absorption is a product of how much air or space there is between the closed cell beads of EPS. It is therefore possible to have foam that has low water absorption and poor fusion, which makes for a poor quality product for use as a surfboard or paddleboard product.
By using a higher pentane EPS foam, the beads are allowed to expand and improve fusion while reducing the porosity of the foam, hence less water absorption.
XPS Foam
XPS stands for Extruded Poly Styrene, and is made from a completely different process than the EPS foam. The XPS foam product starts as a solid polystyrene resin granule, which is then fed into an extruder or die where the granules are melted and then have critical additives mixed with this now viscous fluid. This fluid then has a blowing agent injected to make the material foamable. Under carefully controlled conditions where both heat and pressure are used, this foamable material is then forced through a fixture or die at which time the foaming takes place. The rigid foam is then trimmed into the final dimensions or blocks. This process produces a completely different cell structure to the foam from EPS.
This process provides a material called "Styrofoam", which is a Dow Chemical trademarked name. Mistakenly, most people assume the EPS that is used for coolers and coffee cups is "Styrofoam", but it should be correctly referred to as EPS or beaded EPS foam. Dow has been making the blue "Styrofoam" for well over 50 years, and the material has extensive use in the building trade.
While the material can be used in the production of surfboards, there are some inherent challenges. One problem is that the material is made primarily in 8 ft sheets and only 6 to 8 inches thick. This limits the size of the surfboard that is to be designed. Another problem that can cause issues is the outgassing of the foam over time. This can also cause delaminating of the fiberglass laminate. While some techniques have been developed to minimize this problem, it still remains a challenge. There have been some improvements to the manufacturing process, and the outgassing problem may be minimized and manageable.
Hotwire Foam Cutters
XPS Bonding/Sealer Coat?
