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Difference between Extruded and expanded foam!

Difference between Extruded and expanded foam!

Difference between Extruded and expanded foam!


I am trying to understand what do these two terms mean? They both have closed cell polymer structures?

What kind of foam is used in making the of firm packing foams?

Please correct me if any information is incorrect. Appreciate your help in advance.



RE: Difference between Extruded and expanded foam!

Var 10,
This is as used in packing foam materials, not aircraft structural foams.
Extruded foam ( we are talking Styrofoam here) is a foaming material extruded through a die , it is homogenous. Expanded foam is often called bead board, It is made by steam heating Styrofoam pellets in a die box until they expand and adhere to each other it is not as strong as extruded foam.
Sometimes so called firm expanded foam is a rapid two part polyurethane foam injected into a plastic bag in a box with components to be shipped in the box but separated from the foam by the plastic bag, the foam expands and surrounds the components protecting them from shipping damage.

On aircraft foams, Some PVC foams are expanded foams, where a foaming material is expanded and cured in a box, then sawn into sheets and sections for later use. There are other foams, but if I describe them all I will have several pages here without answering your question.

You are judged not by what you know, but by what you can do.

RE: Difference between Extruded and expanded foam!

Thank you berkshire. So when they say firm packing foam it is just polystyrene extruded through a die?

RE: Difference between Extruded and expanded foam!

var10 (Mechanical)
Yes, if it is a polystyrene extruded foam, go by the weight of the foam in Lbs per cubic foot, the heavier the foam the firmer it is.

Also do not forget the Polyurethane two part packaging systems I mentioned.

One of the newer items on the market is an extruded starch based foam that is bio degradable, it too can be bought in different densities.
Here is a link http://www.starchtech.com/biodegradable-packing-pe...

So if you are packing something to ship, you have to determine what foam you, and the customer want. Be aware that starch based foams do not do well in High humidity.
If you are using this for an aircraft part, then the Blue Dow extruded foam, is most commonly specified for hot wire cutting.


You are judged not by what you know, but by what you can do.

RE: Difference between Extruded and expanded foam!

There is another foam, a polyurethane, that is is actually applied as a liquid foam, http://greatstuff.dow.com/pdfs/factsheet.pdf, which then cures in situ. Typically, as used in packaging, the item is wrapped in plastic and placed into its shipping container, and the foam is sprayed into the cavity between the plastic wrapping and the shipping container walls. This results in a custom fill for arbitrary items being shipped.


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RE: Difference between Extruded and expanded foam!

"Greatstuff" is not the kind of urethane foam used for packaging, however. It is a one-part, moisture curing material used for gap sealing. Urethane packing foams are two-part systems which cure in minutes.

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