Is Styrofoam a Good Insulator? Here’s Why

Styrofoam is used to insulate everything from houses, to coolers to fridges. It's lightweight, cheap and easy to mold into different shapes and sizes which means it is widely used in a variety of places. But is styrofoam a good insulator? How good is it and are there better insulators out there?

Styrofoam is a good insulator because it is filled with billions of tiny pockets of air that are all closed off from each other. It is the air pockets that do the insulating more than anything else, reducing conduction and convection. It has an R value of 0.65-0.7 which is better than cardboard, wool, fiberglass, straw bales, wood, bricks and glass.

What is Styrofoam

Styrofoam is a brand name given to a material called “extruded polystyrene” but when most people talk about styrofoam they are actually talking about the cheap lightweight white insulation that is actually called “expanded polystyrene”.

So for the majority of this article when we talk about styrofoam we will talk about the more commonly used expanded polystyrene, but I'll also make sure to talk about the real styrofoam brand too.

Both of these types of polystyrene are actually plastics that are designed in such a way that they create lots of little bubbles. In fact, styrofoam is actually 95-98% air and only 2-5% plastic. This is what makes them so lightweight.

The cheaper white styrofoam (or expanded polystyrene) is made up of thousands or even millions of little balls that are then stuck together and molded and cut into whatever shapes are required.

This is why you'll sometimes have little balls coming off the styrofoam as it begins to deteriorate.

Why Is Styrofoam A Good Insulator?

The secret to styrofoam being such a good insulator isn't actually the plastic but rather the air trapped inside the plastic.

Air is a poor insulator of heat as most heat needs molecules to move through and in air those molecules are far apart.

Add to it the fact that in styrofoam there are billions of tiny air pockets that are all closed off to each other and you also stop heat from flowing through the product.

Imagine you had a hair dryer and you wanted to make someone on the other side of the room hot. If you could just point it at them and blow the air towards them they will feel some heat. Not a lot, but some.

Now imagine you're standing in a plastic bubble and trying to warm them up. You can't blow the air to them as it'll just bounce off the wall of your bubble.

Now imagine there are 1 billion bubbles between you and the other person. It's going to be pretty hard for that heat to reach them.

In effect, that's how styrofoam insulates.

There are billions of tiny air bubbles that are all closed off from each other so air can't “flow” through the material and neither can heat. That is how styrofoam stops heat through convection (or the flowing of heat).

Air is also a poor conductor of heat so heat struggles to be transferred from one air pocket to the next.

What Is The R Value of Styrofoam

R Values are a way for us to measure and talk about how good of an insulator something is.

Heat transfer is calculated using the following formula:

Heat transferred = surface area x (temperature A – temperature B) ÷ R value

The higher the R value the lower the heat that is transferred.

According to Wikipedia the R value of cheap styrofoam (expanded polystyrene) for an inch of thickness is between R 0.65-0.70 depending on the density of the polystyrene.

The real brand of styrofoam (extruded polystyrene) is a better insulator with an R value for an inch of thickness between R 0.63-0.95 depending on the density.

Compare this to something like cardboard which has an insulation value of R 0.52-0.70 or straw bale which has a value of R 0.25 or glass which is only R 0.025 and you can see that yes styrofoam is a good insulator.

What Insulates Better Than Styrofoam?

While styrofoam is a good insulator it is not the best insulator out there and there are other options that work much better than styrofoam.

The branded styrofoam (or extruded polystyrene) works better than the cheap white styrofoam that is made up of lots of little balls.

Polyurethane, which is the insulation used in Yeti coolers, is also a much better insulator than styrofoam with an R value of R 0.97-1.14

Silica aerogel is better again with an insulating value of R 1.76 but this is extremely expensive and hard to manufacture.

The best insulator is actually a vacuum insulated panel which has an insulation value of R 5.28-8.8 for an inch of thickness. However, a perfect vacuum is nearly impossible to achieve, but you can come quite close.

This is why Hydro Flask bottles work so well at keeping ice for over 24+ hours despite how small they are.

Why Is Styrofoam Used So Much In Insulation?

Styrofoam is widely used in insulation in everything from houses to coolers to fridges as well as other insulating product.

It is so widely used because it is lightweight, cheap, decent at insulating and it can easily be molded into whatever shape you desire.

Better insulators like extruded polystyrene and polyurethane are heavier and more expensive to produce thus aren't cost effective for a lot of different uses.

How Long Does Ice Last in a Styrofoam Cooler?

I've written a full article on how long does ice last in a styrofoam cooler which you can check out but the short answer is “it depends”.

Firstly it depends on the size of the cooler and the thickness of the cooler. Secondly it depends on how much ice you use.

If you use more ice then it your ice will last longer overall than if you use less ice.

However, generally speaking water ice will last 12-24 hours in a smaller styrofoam cooler with a larger styrofoam cooler being able to hold ice up to 3 days if it's nearly completely filled with ice and kept away from super hot temperatures or direct sunlight.

Dry ice last a similar amount of time in a styrofoam cooler and you'll likely get 18-24 hours of dry ice before it's completely gone.

Where Do I Buy Styrofoam Coolers?

Styrofoam coolers are easy to buy and are available from lots of different stores, both online and in person.


One of the easiest places to buy them in from Amazon. They have a wide range of shapes, sizes and different price points.

This is the best place to go to. buy just a single styrofoam cooler or if you’re just buying a few

See the latest prices of Syrofoam coolers at Amazon

Packing companies

If you’re looking to buy in bulk for commercial purposes then your best best is to get in contact with companies that specialize in making shipping boxes and styrofoam containers.

You can get bulk discounts and can get the exact size and shape you need for your business.