What is EPS Foam (Seriously, Why Am I Insulating With Packing Peanuts)?

by Erik North on September 17, 2011

What is EPS Foam


What is EPS foam insulation (also called expanded polystyrene or bead board)? How is EPS foam insulation used in my home? What is the EPS foam’s R-value and how is it different from XPS foam (aka the blue boards in Home Depot)?

And why do I keep saying ‘What is EPS foam’ instead of ‘What is Styrofoam’? First, habit and second, I got tired of paying Dow Chemicals a dollar each time I said it.

When you’ve just received that brand-new computer printer and you open the box, you’ll see that it was cushioned with large white blocks of a molded substance that looks like dense styrofoam. It’s actually a variant of styrofoam called expanded polystyrene. You may have also seen it within your friendly neighborhood (and disposable) coffee cup, not to mention the familiar white squishy packing peanuts.

EPS foam board is similar to XPS (extruded polystyrene) foam insulation. Both EPS and XPS work really well as insulating foams, as you can see in the case of a coffee cup.

What is EPS Foam – a Wikipedia Style Definition

(An aside about this section…I copied and modified it from the XPS section as the two insulations are extraordinarily similar). EPS stands for Expanded Polystyrene. EPS foam board is essentially liquified then molded and compressed styrofoam. Ever grab your Dunkin’ Donuts coffee and not get burned? Well the hot coffee is kept from scalding your mitts by 1/4” of polystyrene foam. Imagine how well 2 or 4 inches would insulate (Answer: much better).

EPS foam board is an insulation material similar to polyisocyanurate and XPS foam board in its texture and rigidity. It is usually white with a smooth beaded surface.

Polystyrene is liquified to create EPS. This liquid is expanded and congealed as individual beads then molded in a shaped form. Once hardened, it is cut into the 4’x 8’ sheet boards that most customers have seen at Lowe’s as they walk past it to buy fiberglass.

EPS panels can come unfaced or faced typically with a foil air/vapor barrier. The R-value is about 4 per in. This type of rigid foam won’t absorb water and can act as an semi-impermeable vapor barrier. EPS is less rigid and less durable than XPS foam board and it is less expensive that polyisocyanurate.

What is EPS Foam – Where Can I Find It?

You can find EPS foam board in home department stores like Home Depot or Lowe’s. It is sold in 4’x8′ rigid boards typically either 1″ or 2″ thick and may be called “bead board.” EPS foam board, like XPS, is great for insulating walls in places like cellars, garages and attics. It can also be cut and attached under eaves.

What is EPS Foam – Many Insulation Options

So…what is EPS foam? It is one of many types of insulation that are available to you as a homeowner. EPS foam has a solid R-value and unlike fiberglass or cellulose, can be used in high humidity siuations safely. All of these types contribute to giving you some level of financial payback when it comes to your heating bills.

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