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Does Styrofoam Keep Things Warm?

Many people have heard about “insulators” in school science classes: those things that, among other things, help keep things warm. And among materials that keep things warm in the world, they do say Styrofoam keeps things warm, right? 

Styrofoam keeps things warm because it’s made out of polystyrene foam, which has many trapped pockets of air. Air doesn’t allow heat to pass through it too well, so the air pockets in styrofoam insulate whatever is in the container and prevent heat from escaping. 

However, there’s a common mistake made about the term ‘Styrofoam’ when people discuss material that keeps things warm. In this article, you’ll find out in detail about just what Styrofoam is, what the mistake is, a warning, and the full science behind just how Styrofoam keeps things warm.

Does Styrofoam Keep Things Warm?

Just what is styrofoam?

Styrofoam is actually the trademarked term for the petroleum-based plastic foamed material known scientifically as polystyrene. It is manufactured by the Dow Chemical Company. Dow owned it since 1947 when it was patented after researchers in Dow’s Chemical Physics Lab found out how to make it, rediscovering a method first used by Swedish inventor Carl Georg Munters.

Styrofoam is very effective as an insulator, and so it is one of the most common plastics used in the making of plastic insulating materials.

Styrofoam is great at stopping the transfer of heat. That particular type of insulation is called “thermal insulation.” As a result, the practical application of Styrofoam is in making insulation boards that will function in fact as building insulation boards in the walls, roofs, and foundations of houses. Apart from building insulation sheathing of this sort, it is also used in pipe insulation.

Styrofoam is readily identifiable by its light blue color. So it is commonly called “Blue Board.”

Are there different types of styrofoam?

When people ask the question, “does Styrofoam keep things warm?”, they might not always be talking about the same Styrofoam. As you’ve seen above, Styrofoam is technically a trademarked term for material used in building. But there’s a mistake people make.

In many places in the world, colloquially, ‘styrofoam’ is a word that is just used casually to refer to another material that is white in color and also made of polystyrene foam–though not by the same process. It’s most commonly used in food containers and coffee cups and packaging to keep stuff like food or coffee warm. What’s happening here is a case of a trademark becoming generic

That is a mistake. Because this material is completely different from the polystyrene used in proper Styrofoam insulation, even though this material often mistakenly referred to as ‘Styrofoam’ also does keep things warm.

The Dow Chemical Company says that there isn’t a coffee cup, cooler, or packaging material in the world that is made of Styrofoam. The material thought to make up such items, often thought to be Styrofoam, is thus emphatically not Styrofoam. The material confused with Styrofoam, the Dow Chemical Company says, ought to be referred to by the generic term “foam.”

A Warning

While you’re reading this, a word to the wise: it would be most unwise to keep beverages in cups of the type of material that’s mistaken for “styrofoam.” Polystyrene, no matter, however much it helps to keep things warm, contains the substances Styrene and Benzene. 

Does Styrofoam Keep Things Warm?

These are extremely toxic substances for human beings. They are suspected carcinogens (substances that cause cancer) and neurotoxins (substances that damage nerve tissue).

The hot foods and liquids people put in thinking such foam will keep them warm actually starts a partial breakdown of such foam. This causes the toxins present in them to get dissolved. When they are put to the lips, one absorbs the toxins into the bloodstream and tissue.

In any case, a thermos flask or container will capture heat by a margin much more than that by which such foam will keep things warm. While the ability of this kind of foam to keep things warm is in itself good, it absolutely pales in efficiency and effectiveness when faced by this rival. When there is a better alternative, wouldn’t it be a good idea to consider it apart from any other concern, anyway?  

How does Styrofoam keep things warm?

Styrofoam is made mostly up of air: around 98%. Air is extremely bad at conduction, but good at convection.

According to the law of conservation of energy, the total amount of energy in any system cannot get created or destroyed. So, let’s say one is looking at heat energy in a particular system: the heat energy cannot get “destroyed” and does not, let’s say, melt away by itself. By itself, it remains constant. It can only be “lost”: the heat energy can move on away from a hotter object to a colder one. 

For Styrofoam to “keep something warm,” then, means that the transfer of heat from the object to any other object outside or around it that is lower in temperature has got to be stopped. Then, by the property of energy remaining constant and not getting destroyed, the heat will stay “stored.” In a nutshell, that’s basically how the process of insulation works.

Does Styrofoam Keep Things Warm?

The ‘transfer of heat’ can happen through conduction or convection.

Conduction occurs when heat energy can escape away, flowing from a hot object to a colder one when the two of them are in contact with each other, physically touching each other. (How fast this happens depends on stuff like the temperature difference between the two objects, and a whole lot of other stuff.) As has been noted, air, which is the major constituent of Styrofoam, is not a good conductor.

Convection is heat transfer due to the bulk movement of molecules (molecules are the tiny things all matter is made up of). It happens when some of the molecules of the material flow from one place to another, and the heat energy is carried along in this process. But air is a good convector, right? So then how does Styrofoam insulate?

Well, the process by which Styrofoam is manufactured makes it trap air in small ‘pockets’ or ‘bubbles.’ This prevents air from being able to flow in any proper way. As a result, the heat transfer becomes negated to minimal because the low mass at any one fixed particular point can’t store much of an amount of heat. This effectively blocks the flow of heat energy via convection too. 

Thus, both conduction and convection get taken out of the equation. As a result, Styrofoam is a good insulator.

Does Styrofoam Keep Things Warm?

Styrofoam is typically placed in wall cavities in order to keep the insides of buildings warm. By trapping air and reducing the transfer of heat energy, it keeps the necessary heat inside the building. If, on the other hand, the material used in the building in these constructions had been metal, that would have been a bad idea. This is because metals usually allow heat energy to flow through them, and are thus bad “insulators.”

Other major applications of the property of Styrofoam to keep things warm include:

  • Roof and floor
  • Basements
  • Insulating concrete forms
  • Exterior insulation and finish systems
  • Acoustics and sound impact

In sum then, Styrofoam does keep things warm because:

  • Styrofoam is polystyrene foam.
  • It is composed of around 98% air.
  • Air is a bad conductor of heat, but a decent convector.
  • Styrofoam is made in a process that creates a material that traps air in bubbles or pockets.
  • Convection also gets stopped.
  • Heat is prevented from escaping.
  • As a result, Styrofoam keeps things warm.

So now you know what Styrofoam is, and how it does what it does in keeping things warm. Crucially, hopefully, you’ve also learned now about the common mistake people make about the particular Styrofoam one is talking about when discussing the question “Does Styrofoam keep things warm?” and about the harmful effects that that other warm-keeping foam can have.


  • Jake Alexander

    Jake is a freelance writer from Pennsylvania who enjoys writing about science and sports. When he's not writing for Temperature Master, he can be found watching the NFL or playing basketball with his friends.

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