What are the Pros and Cons of Polystyrene Insulation?

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  • Written By: Lori Kilchermann
  • Edited By: Lauren Fritsky
  • Last Modified Date: 23 February 2019
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Polystyrene insulation is a type of insulation commonly found in home construction. The lightweight material is less irritating to install than fiberglass and is easily cut to fit into walls and ceilings. Its insulating factor is far less than a comparable fiberglass bat, however. One advantage that it offers is that it is relatively inexpensive. Perhaps the greatest disadvantage with this material is its inability to absorb moisture.

Insulation does two things when properly installed: it retains heat in the winter and reflects heat during the summer. While fiberglass insulation is most commonly known by the average homeowner, polystyrene insulation is a viable option for most insulating needs. It does, however, have some drawbacks and benefits that should be investigated prior to its installation. The ease of installation and lack of skin irritation is one benefit of using polystyrene. Most commonly known as pink or blue board Styrofoamâ„¢, this insulation comes in large square sheets that are scored with a knife for easy separation in intervals that match most common stud spacings.


The easy separating construction is an advantage to this type of insulation, and it is responsible for time savings in many installations. The board-like configuration prevents it from sagging and falling over time, which helps prevent hot and cold spots in any given exterior wall. The most problematic trait of the Styrofoamâ„¢ board is in its inability to wick moisture out of the structure. The smooth finish on the foam board is resistant to water; therefore, any moisture trapped in the wall will remain in the wall without a way to be vented away.

Another disadvantage with the polystyrene insulation is its incompatibility with most electrical wiring. The protective plastic coating used on most common electrical wiring will erode prematurely if it comes into contact with the foam insulation. This can lead to electric shock as well as fire that could potentially injure or kill occupants of the structure and could result in loss of the structure itself. Some manufacturers offer wiring with a special purple coating that will not be damaged by the insulation, but this can eliminate any cost savings from using polystyrene instead of fiberglass insulation.

This type of foam insulation also has relatively low insulating properties when compared to fiberglass bat-type insulation. The polystyrene must be applied in several layers in order to achieve the same rating as a single bat of the fiberglass mat. When installed between a structure's roof rafters, however, the foam does add a layer of insulation that is energy-saving and efficient.


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Post 3

@Mor - The problem is that bales of straw aren't very durable, even if they are eco-friendly. I don't know how you could treat them to the point where they wouldn't eventually start to rot.

There are pluses and minuses to all kinds of insulation, but it's always been my understanding that most insulation (even more modern types, like rockwool) is made from recycled materials anyway, so you should be able to have your cake and eat it too.

Post 2

@irontoenail - The problem with that is that most supply stores will give you a discount the more you buy, so buying two different kinds of insulation isn't going to be very efficient. Of course, if you are getting your supplies through a builder or something, they might still be able to get a bulk deal and just use the extras on a different house.

Personally I don't like either of these kinds of insulation. They are both quite unnatural and dangerous, the styrofoam because of the wiring and the fiberglass because of the air quality. I recently saw a show where they built a house from straw bales and that's supposed to provide excellent insulation. I'd much rather have something like that for my house.

Post 1

It doesn't sound to me like it's worth getting the polystyrene insulation, although I wonder if it depends on where you're putting it. There are probably places in the house which need the bat style insulation more than the styrofoam insulation and you could just get some of each type and use it accordingly.

I've definitely seen people use the sytrofoam insulation when insulating the floors of older homes in a cheap upgrade and if your home doesn't have wiring running throughout the floors that can be a good option. It seems to be easier to install as well, and, depending on the climate and your home type, of course, you probably don't need as much insulation installation in the floors as in the walls.

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