Extruded foam
differs from expanded foam found in Styrofoam cups.
Foam tops some drinks, like beer. But beer foam isn't the same as plastic foam, which is what you find in your summer ice cooler or the blue wraparound Dow Styrofoam container for your canned soft drink. Ice chest container foam is really a foam plastic made from polystyrene and polyethylene. These poly compounds can be melted into a liquid -- extruded (stretched) -- during the manufacturing process or expanded (molded into shapes using heat).
Extrusion Process
Polystyrene is a solid crystal (also known as a resin granule). Combining polystyrene granules with additives in an extrusion machine results in a hot liquid. The extrusion machine acts like a large-scale blender, much like that in your home, except it is temperature-controlled. The crystals and additives need extremely high temperatures to meld together in this manufacturing blender. The heat helps melt the crystals and blend them with the additives to produce a liquid foam product. The extruding machine pours out the foam liquid into dies based upon the desired shape of the finished product, and it is left to cool.
Significance
Extruded foam products differ from foam products made through expansion of polystyrene crystals (or beads, as they are sometimes referred to). Expanded polystyrene -- made through a process in which polystyrene crystals undergo simultaneous pressure and heat to push the beads together into a molded shape -- is not as strong, as water resistant, nor as well-insulating as extruded polystyrene.
Uses
A good example of the different properties between extruded foam and expanded foam can be seen when looking at their uses. Extruded foam is used extensively in the construction and engineering fields. Buildings need materials that can resist water absorption, insulate well against heat and cold and be durable. Extruded foam has those capabilities. Expanded foam, on the other hand, performs well as your coffee cup or the foam craft shapes you use. Both foam types are also used in bedding products.
Warning
Don't expose extruded foam to any open flame or potential combustion source. In interior applications in the home or office, extruded foam should never be left exposed as long as people live or work in the area; instead, attach a half-inch gypsum board over the foam.
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