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Old 09-29-17, 02:12 PM   #29
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Originally Posted by ecomodded View Post
I was thinking to myself they use spray foam under houses foundation I should check on the psi of the wall board and yup its tough enough.

You used the XPS 1000 for your foundation or equivalent hey ? I know little about the XPS / EPS but need to learn it.
The main difference is in the manufacturing process used for each foam.

EPS starts with a bunch of tiny polystyrene beads. They pour them into a mold and then heat it all up with steam or hot gas. The beads expand and bond together. That's why most styro-foam packaging and the EPS foam looks like it was made from a million little tiny BB sized beads. It has voids that don't completely close and when you break it, it breaks along those random voids.


XPS foam starts with melted polystyrene. They agitate it and foam it with a gas as it is forced through an extrusion die and cooled. The extrusion die can be of any 2 dimensional shape and the 3rd dimension is a continuous length.

For boards, planks, rounds and other simple shapes, the extrusion process is great. The density of foam can be controlled by foaming it with more or less volume of gas. Also, it is one big contiguous structure of polystyrene with air bubbles.

For complex shapes, the mold filled with beads used in the EPS process is extremely versatile. EPS foam is used in the lost-wax or investment casting process for automotive aluminum parts. You can see the EPS foam bead texture carried through from the foam pattern on plenty of aluminum cylinder heads and engine blocks.

In reality, the two types of foam are almost the opposite structure of each other. XPS (extruded foam) is a big block of polystyrene with air bubbles (tiny spherical voids). EPS (expanded foam) is a bunch of tiny spheres packed closely and expanded until they touch each other and bond together.
(Of course, it is true that each bead has a bunch of little air-pockets inside it from the steam or hot gas).
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