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What is Foam Board Insulation?
Foam board insulation is a sheet, usually four by eight feet (1.2 by 2.4 m) in size, of rigid foam used in nearly all aspects of building construction to provide thermal resistance in floors, ceilings and walls. Basically, three materials are used to make foam board: polyurethane, polyisocyanurate and polystyrene.
Polyurethane and polyisocyanurate foam board are very similar in content. The closed-cell foam board is made by first liquefying the pellets, and then introducing a blowing agent. In the case of these two products, the blowing agent is usually one of the hydro fluoro compounds (HFC) or chloro fluoro carbons (CFC). The blowing agent forms gas bubbles in the mixture when it is heated. The hot, liquefied polyurethane or polyisocyanurate is then forced into a board-shaping dye. After the mixture cools, it is cut into any desired length. The resulting foam board insulation is of higher R (resistance to heat flow) value than a polystyrene foam board, usually R7 or R8 per inch (2.54 cm) of thickness.
Polystyrene foam board insulation is made in much the same way as Polyurethane and polyisocyanurate foam board, except for the differences in expansion. There are two basic types of this type of insulation: molded expanded polystyrene (MEPS), and extruded expanded polystyrene (XEPS). The difference in these two types of foam board is the strength of the finished product, though the density, about 1.5 pounds per cubic foot (0.21 kilograms per cubic meter), is usually the same.
MEPS foam board insulation, often called beadboard, is made by mixing unexpanded polystyrene pellets or beads containing pentane with a blowing agent. The resulting mixture is poured into a closed container and heated. The heat causes the beads to expand to many times their normal size. The mixture is then poured or injected into a mold, more heat is applied, and the resulting foam blocks are shaped into insulation.
XEPS is made by mixing polystyrene pellets with chemicals to liquefy them. Once a blowing agent is injected into the mixture and it is heated, gas bubbles form, and the hot material is poured into forms. When cool, it is cut into whatever shapes desired. XEPS is stronger than MEPS, having higher compression strength. Because of its greater strength, XEPS foam board insulation is often used for roofs and walls in new construction. The extruded polystyrene also has a higher rating for resistance to moisture.
Both MEPS and XEPS have lower R-values than Polyurethane and polyisocyanurate foam board insulation, rating about R5 per inch (2.54 cm) of thickness.
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![Artists use polystyrene foam board.]()
By: Museum of VancouverArtists use polystyrene foam board. -
![Polystyrene -- often associated with insulation -- can be used to make foam-board insulation.]()
By: brozovaPolystyrene -- often associated with insulation -- can be used to make foam-board insulation.
Discussion Comments
I thought this was really interesting. I always wondered how they make this type of insulation. I never realized there were so many different types, either. I'll have to keep all this in mind if I ever need to buy insulation.
The stuff I have seen before has always had some sort of foil or reflective material on it. What is the purpose of the foil faced foam board insulation, and how do they make it?
The article talks about polyurethane and polyisocyanurate foam boards being made with HFCs and CFCs. Aren't these things really bad for the environment? I actually thought they were outlawed for use. Does polystyrene insulation have them, too? The article doesn't directly mentioned them.
@matthewc23 - Good question about the attic insulation. I remember thinking that when I was insulating my attic. Really, there is no difference as long as you are getting the R value you should have. The big difference is in price and ease of installation.
The rolled fiberglass batting can have a much, much higher R value than foam board insulation. You can find foam board that is four inches thick or so, but it can get pretty expensive at that point.
Installation is also easier with fiberglass. With foam board you are either supposed to glue or screw the insulation down and caulk around all of the edges. With the rolled fiberglass, it is large enough to fill its entire space and you can keep it in place with staples. That makes it a lot easier to take out if needed.
So, I know someone who just put foam board insulation panels down under the floor of his attic. Any time I have seen this done, it has always been with the rolled batting type of insulation. Since foam board insulation seems so much easier to use, why would anyone ever use the rolled batting that is so itchy?
The article also talks about the difference in strength of the various types of insulation. Does it really matter when it is going to be put into a wall anyway? It isn't like anyone is going to be messing with it a lot.
Also, does anyone know what MEPS and XEPS stand for? I am just curious.
@Ivan83 - It has been a while since I replaced the insulation in my attic, but I don't remember it really costing that much. I think it might be six dollars or so per sheet of insulation. That all depends on the thickness you get, of course, but from what you described, I think something that is an inch or two thick would be good.
If you search online, you can find calculators that will help you choose the right R value to pick based on your zip code. It really all comes down to the R value in the end. There is no reason to pay more for one type of insulation over another if they both have the same R value unless you're looking for a specific kind like MEPS or XEPS.
I'm hoping someone here can help me. I am trying to insulate my attic. I am not a handyman but I am not totally inept either. I am pretty sure that I can install some foam board insulation by myself.
The problem I am having is trying to select the right kind of insulation. I live in Oklahoma where it gets pretty cold in the winter and pretty hot in the summer. What is the best kind of foam board insulation to use? I know that I don't need the most heavy duty stuff but I also don't want to use the cheapest and thinnest. So what should I look for and what is a good price to pay for it?
I've installed a lot of insulation in my time and foam board is really the only way to go. It is so much easier and cleaner to work with than some of the spray and rolled insulation you used to see a lot.
It is also a lot easier to transport. You can fill the bed of a truck with the stuff and travel down the highway without worrying about it. I only mention this because one time I lost a bunch of fiber glass insulation on the highway. I didn't realize it was gone until I got to the job site like an hour away. Boy I was steamed about that.
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