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What is Polystyrene?

Karyn Maier
Updated May 17, 2024
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Polystyrene is a type of polymer with thermoplastic properties produced from the petroleum-derived monomer, styrene. In solid form, it is a colorless and rigid plastic, but it may also be returned to a liquid state by heating, and used again for molding or extrusion. It is used to produce many products for industrial and consumer use. In fact, its presence as a plastic in everyday life is second only to polyethylene.

The chemical structure of this material allows it to be classified as a liquid hydrocarbon, meaning that it is composed exclusively of hydrogen and carbon. Like its precursor, it's an aromatic hydrocarbon that participates in covalent bonding with every other carbon atom being attached to a phenol group. It is produced via free radical polymerization, which means that the reaction involves breaking the bonds between electrons and leaving them “free” to form new bonds. When burned, this material yields black carbon particles, or soot. When completely oxidized, only carbon dioxide and water vapor remain.

There are several different types that are produced. Extruded polystyrene is considered to have as much tensile strength as unalloyed aluminum, but it is lighter and more elastic. This is the material used to make a variety of molded products, ranging from plastic tableware to CD cases and model cars. It is also used to produce medical and pharmaceutical supplies.

Extruded polystyrene foam, commonly known as Styrofoam™, is a type of insulation with versatile applications, such as the manufacture of surfboards. In fact, its buoyancy prompted the U.S. Coast Guard to adopt its use in life rafts. This type may also be used in building materials or in roadway construction. For example, it may serve as a layer of insulation under pavement to prevent freezing and thawing of the soil below from cracking the surface.

This strong but lightweight material is also used for crafts, and it is usually sold in sheets. It is typically made up of three layers, with polystyrene at the core sandwiched by paper on either side. The sheets are frequently used as backing to mount artwork or photography, or to construct architectural models. This foam is also familiar to those who work with floral crafts. In fact, the characteristic “crunch” sound made when it's cut is well-known to florists.

Expanded polystyrene foam is actually made of beads of the material. It is used to make “peanuts” for packaging, disposable coffee cups, and foam picnic coolers. Unlike extruded foam, which is blue in color, expanded foam is typically white.

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Karyn Maier
By Karyn Maier
Contributing articles to About Mechanics is just one of Karyn Maier's many professional pursuits. Based in New York's Catskill Mountain region, Karyn is also a magazine writer, columnist, and author of four books. She specializes in topics related to green living and botanical medicine, drawing from her extensive knowledge to create informative and engaging content for readers.
Discussion Comments
By healthy4life — On Aug 29, 2012
My friend has polystyrene insulation in his house, and he always has a lower electric bill than I do. However, he says that it costs more than other types of insulation.

Since I rent a home, I don't really have to worry about picking out insulation right now. If I ever do, I will look into polystyrene. It would be so nice to save money on heating and cooling, even if the cost at the upstart was a bit higher.

By DylanB — On Aug 29, 2012

The break room where I work keeps polystyrene cups on hand. People use them for coffee and water, so they are suited for both hot and cold drinks.

It always seemed strange to me that foam cups could hold something as hot as coffee. I know that when I tried to use a hot glue gun on a piece of foam, it melted away. It's hard to believe that coffee fresh from the pot doesn't melt the foam.

By Perdido — On Aug 28, 2012

@Oceana – Polystyrene will deteriorate if it isn't sandwiched between protective layers. If it starts to come apart, then the work of art it holds will be vulnerable to bending.

The safest polystyrene to use is foam board. It is covered on front and back, and you can get an acid free version to protect your daughter's artwork.

I've heard that polystyrene is sensitive to sunlight. So, hanging the artwork near a window wouldn't be a good move.

By Oceana — On Aug 27, 2012

Is there a reason that the polystyrene material used as backboards for art is covered on both sides by paper? Would it somehow mess up the artwork if it came in contact with the drawing paper? I have a polystyrene sheet that I have considered using as backing for some of my daughter's drawings, but I don't want it to destroy them.

By anon150729 — On Feb 08, 2011

Yes and it makes up for 80 percent of the pollution in the world's oceans.

By anon75026 — On Apr 05, 2010


By anon75025 — On Apr 05, 2010

it's so informative and so detailed.

By anon31531 — On May 06, 2009

Is polystyrene a natural or synthetic substance?

Karyn Maier
Karyn Maier
Contributing articles to About Mechanics is just one of Karyn Maier's many professional pursuits. Based in New York's...
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