Open vs Closed Cell Spray Foam Insulation | What's the difference?

What's the difference between open and closed cell polyurethane spray foam insulation? In this video, we discuss how it's made, their performance and properties. We’re going to find out if one is better than the other and where you should use them.

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Chapters:
0:00 Introduction
0:37 How it's made
2:50 Appearance
3:58 R Value
4:46 Heat Transfer
6:03 Water resistance
7:07 Insulation4US
7:53 Fire resistance
8:53 Cost
9:13 Uses

Both open and closed cell polyurethane spray foam is made of 2 parts.
Part A contains very reactive, low molecular weight chemicals called isocyanates which have a nitrogen-carbon-oxygen group. These can be methylene diphenyl diisocyanate (MDI) and polymeric methylene diphenyl diisocyanate (pMDI). Part A is standard for all manufacturers.

Part B is a proprietary blend of chemicals that provide unique properties in the foam. It contains a polyol which is an organic compound containing hydroxyl or OH- groups. It also contains initiating catalysts which help the reaction occur, curing catalysts that allows the reaction to continue to its completion, flame retardants that prevent the start or slow the growth of fire, blowing agents that form the gaseous part of the foam and surfactants that reduce surface tension of a liquid and encourage foaming.

In open cell spray foam, the bubbles rupture, leaving behind only the struts or the points at which two bubbles touch each other. In closed cell insulation, the bubbles don’t rupture, creating interconnected closed pockets with trapped blowing agents. Open cell spray foam uses water as a blowing agent while closed cell spray foam needs a chemical blowing agent.

Open cell spray foam expands over 100 times its liquid volume so it can insulate hard to reach nooks and crannies. It is oversprayed and then shaved down. It is soft and flexible. It has a low compressive strength and can be easily punctured and pierced. Closed cell spray foam expands about 30-40 times its liquid volume so it is good in tight spaces, where space is an issue. It is undersprayed because it cannot be shaved down easily. It is hard and doesn’t compress. Open cell density 0.4 to 1.2 pounds per cubic foot while closed cell spray foam has a density of 1.75 to 2 pounds per cubic foot.

They have a high R value which is a measure of resistance to the flow of heat. The higher the number, the greater the insulating power. Because it doesn’t contain any trapped air, open cell spray foam has a lower R value of 3.5 per inch. Closed cell spray foam has a higher R value of 6 per inch.

Open cell foam has a perm rating of around 15 for a 2” depth so it cannot block water vapor. Closed cell foam acts as a vapor barrier when thick enough, over 1.5”. It has a perm rating of less than 1 perm for a 2” depth.

Both open and closed cell polyurethane foam are thermoset materials. They will char and flake when burned, but will not melt and drip like a foam coffee cup. They meet Class I fire standards, they have a flame spread index of less than 25 and a smoke developed index of less than 450.

The cost of both open and closed cell foam has fluctuated wildly over the past year because of raw material shortages and supply chain issues. A rough estimate is 50 cents to 1 dollar per board foot of open cell spray foam and $1.5 to $3 for closed cell foam.

Open cell is good for soundproofing. It has about twice the sound resistance in normal frequency ranges as closed-cell foam. Open cell is better in warm climates where the inside of the structure needs to be kept cool. In the states, that includes climate zones 1 to 4. Closed cell foam which has a higher R value is better in cold climates when the inside of the structure needs to be kept warm. In the states, that includes climate zones 5 to 8 and marine 4.
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