How Styrofoam Cup Insulation Works
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Polystyrene
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Styrofoam is a brand name of polystyrene patented by the Dow Chemical Corp. The name also is used as a general term for "foam" cups, packing material and food containers. Polystyrene is a polymer, or long chain of molecules, that are strung together into a clear fluidlike substance. The polymer is then injected with gases to make it "foam" up and turn white. Injected gases turn the fluid into separate strings in the same way that fluidlike dough can be made into noodles; it separates them and makes them into individual, thick strands. The introduction of gases and the separation of strands are important steps to polystyrene's ability to insulate.
Gases
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In general, solids and liquids are very good conductors of thermal energy. Gases, however, are not. When gases are injected into the liquid polystyrene, they become trapped inside the resulting foam, forming little bubbles. If we continue the noodle analogy, the gases inside are the spaces between the noodles when the strands are put into a sealed container. They are not part of the noodles, but take up room and keep the heat contained in the noodles.
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Increased Surface Area
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The strands of polystyrene have an increased surface area on the inside. Like the noodle example we used above, there is a lot more surface area in the pasta than in the dough. This means that thermal energy must move great distances before it can travel to another strand; more than if the polystyrene were still fluidlike. The long distances, added to the trapped gas bubbles, makes polystyrene, or "Styrofoam," an excellent insulator.
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