R-Value of Polystyrene foam Peanuts
Name: Renet D.
Date: February 2004
I have a 12 x 15 shed completely unfinished inside. I would like to create an art studio space
which I will use year-round and need to do it as inexpensively as possible. I would like to
cover the studs with wood lathe and pour used Polystyrene foam packing peanuts into the cavities. I
figured if I start now (February) and spread the word in the community I can accumulate enough
to finish by next fall. I am wondering what R-Value I can expect from this method and how
densely I will need to pack the peanuts. I may also add a layer of burlap over the entire
walls. Am I crazy? LOL! My husband just answered that one and he is no scientist!
I am home schooling 2 of my sons (ages 7 & 8) and am registered to do so in Delaware
(StonesThrow School #DOE code 9162) if that helps. The boys will be the primary users of
this space, and 'recycling' is our theme for its creation. Hope that makes it possible to
gain your assistance, but thank you for your reply if not.
As a professional civil engineer, I recommend against using packing foam for building purposes
in the strongest possible way. This is a DANGEROUS idea. Foam panels sold for insulating
buildings are treated with flame retardants while it is likely that foam peanuts are not.
Untreated Polystyrene foam is dangerously flammable and produces highly toxic fumes. I expect that
burlap is also not fire resistant. You do not want to use these items to insulate an occupied
space!!! Fiberglass or commercial foam insulation is not that expensive and you will not have
to spend anything on wood lathe.
You may recall the tragic nightclub fire in Rhode Island recently. Although I am not
personally familiar with that case, I have read news accounts saying that the club's owners
had lined the walls with foam egg cartons for acoustic purposes and that material's
flammability had greatly contributed to the severity of the fire and toxic smoke. That
material is the same as used to make foam peanuts.
If you want to recycle, there are inexpensive cellulose insulating materials made of chopped
newspaper you can use in the same manner you want to use the foam peanuts. These materials
are treated with a fire proofing agent that makes them safe for this purpose.
Andrew Johnson, Ph.D., P.E.
I think that Polystyrene foam "peanuts" would make good insulation, although I do not know what the
"R" rating is. My concern would be one of fire safety. I do not think that Polystyrene foam "peanuts"
are fire retardant, and if they are not a fire might be a serious danger. You should check with
your local fire department and/or zoning board about regulations regarding their use in
building construction. They may not meet code requirements. I do not know.
I can give you some comparable "R" values of the following insulating materials:
A. 1 inch Polystyrene (Polystyrene foam) insulation board-3.6.
B. 2.5-3 inches of fill material (Polystyrene foam)-7.0.
C. 3.75-5 inches of fill material (Polystyrene foam)-11.
I hope that this helps. If you need detailed heat transfer formulas, please let me know and
I can give them to you.
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Update: June 2012