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Open Cell Spray Foam vs. Closed Cell Spray Foam

Closed vs. Open Polyurethane Spray Foam

By David Braddy LEED GA

Last month we discussed the benefits of a hot roof system using either open or closed cell spray foam. If you missed it you can read it at http://LakeEcoGroup.com

Let’s also keep in mind that insulation is the key to energy savings and a cornerstone of an eco-friendly building.  Sustainable building practices require that we reduce the heating and cooling loads as much as possible. Many of the guidelines and codes used just a few short years ago simply do not cut it anymore, and the excuse “we have always done it that way or that’s how I was taught” doesn’t cut it either.

Central Heating and Air Conditioning Systems changed building methods forever, we are now starting to understand how this contributed to unhealthy homes by the formation of rot and mold in the building envelope.

Insulation has always been the thermal barrier of the building and we have typically focused on the R-Value of the insulation material only. This is simply the resistance of heat flow through the building envelope. Unfortunately this can be very deceiving because it is only part of the equation. How effectively insulation blocks the flow of air and moisture is equally important and R-Value means very little if you do not have an effective air and moisture barrier.

Most of you would be very surprised at how little energy it took to heat and cool a properly insulated and sealed home, and yes there are now ways to fill and seal existing wall cavities.

Energy Efficiency is why spray foam has become so popular, there are 2 types open and closed cell.

They are both superior products to conventional insulation methods, both are great air barriers. The major difference is in the R-value per inch and moisture permeability. The R-Value per inch of open cell is approximately 3.8 and the R-Value per inch of closed cell is almost double that at approximately 6.8 per inch. Closed cell spray foam also adds to the strength of a structure because it bonds to and becomes part of the structure. Closed cell is a true air and moisture barrier at 2 inches.

Do not believe any salesperson, trying to sell you open cell that says, “Since closed cell is solid, normal building movement will make it break lose”. This is simply not true, if applied correctly closed cell will greatly improve the structural integrity of any building and becomes part of the structure, it will not break lose.  Also do not believe a salesperson trying to sell you closed cell when he tells you that “open cell will wick water because it is sponge like”, it will only wick water when the cell structure is damaged. These are both sales tactics to sell one over the other.

Here is a comparison of moisture perm rating, the higher the rating the more moisture can pass through

  • Closed Cell has a perm rating of 1 for a 2” thickness
  • Open Cell has a perm rating of 10 for a 5” thickness
  • An unfaced fiberglass batt has a perm rating over 100

So which one is better? As you can see closed cell wins hands down for structural integrity and moisture resistance, but it will also be the more expensive of the two, they are both superior to conventional batts.  There is really no way to tell you which one is better for your particular situation. I am partial to closed cell as the better product, but it is more expensive. For sound control I would opt for open cell as the better product. Now if moisture was not an issue and I didn’t care about adding strength to my structure I would probably again opt for open cell. Climate will also play a role in this decision.

The people you consult should have a thorough understanding of local climate and building science, unfortunately many people in the industry do not have this expertise or are very resistant to change. This is why we still have musty, moldy, rotting homes. A properly sealed building envelope will not have these problems.


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