QUALITY SERVICE SINCE 1989
Spray Foam 101
The Wonderful World of Foam for Beginners
by Pat Dundon
Dundon Insulation, Inc. dba The Insulation Man
428 Court St, Suite 2
Binghamton, NY 13904
Phone: (607) 775-3035
Fax: (607) 775-3045
Pat Dundon is the President of Dundon Insulation, Inc. He does business as "The Insulation Man" from a base in Binghamton, NY. His company has been spraying foam since 1993 in residential and light commercial applications. He also offers building science diagnostics, and his firm uses cellulose where it is applicable in his projects.
This article describes his personal experience with spray foam over the past 20 years, and it represents his opinion; it is not a scientific report or a technical evaluation. His objective in taking the time to compose this article is to share his personal experience over the past twenty years.
The Building Performance Contractors Association of NYS is grateful to Pat for his willingness to share his experience. Questions about particular products should be addressed to manufacturers. Specific questions about applications should be referred to Code Officials or technical consultants. Many people feel—when it comes to spray foam insulation in Central NY-- that Pat’s opinions are well worth reading.
I'm going to try to give you an understanding of Spray Polyurethane Foam insulation: the good, the bad, and the ugly. I‟ll also explain the difference between open cell and closed cell, but first I‟ll discuss the things that are generic to all types of spray foam.
There are two primary categories of spray foam in the market today, urethane and urea formaldehyde or Tri Polymer Foam. They are very different products.
Urea formaldehyde was commonly installed in the 70's. It can be recognized as a white, fine-grain foam product that will become friable with minimal agitation. It is normally injected, not spray applied. It is physically much like the foam florists use to keep cut flowers arranged in a pot, but it is white.
Spray Polyurethane Foam is a 2 part chemical using primarily a Polymeric MDI hardener and one of several polyols consisting of some petroleum, either recycled or virgin, some agricultural oils, water, surfactants, amine based catalysts, fire retardants, and likely some products not known by me, but absolutely no Formaldehyde. The best place to learn about foam in more detail is Sprayfoam.org.
This article is about Spray Polyurethane foam, and my objective above was to establish that Spray Polyurethane foam and Urea Formaldehyde foam are very different products with no similarities except the name foam.
Urethane is a two-part system that is much more restrictive on ratio. If you do not deliver the components in the correct proportions, you get poor adhesion and you commonly get poor cell structure. Urethane is usually spray applied, not injected, so you can see what you are doing. Urethane application machinery uses a single-drive cylinder to push product through two material delivery cylinders. The delivery cylinders are of equal volume. It is pretty hard to get an off-ratio mix with urethane. Off ratio product can happen though. Doughy or rubbery SPF is resin rich, crisp or friable foam is Isocyanate rich. Neither is acceptable in any house.
For residential applications, urethane is usually marketed as "open cell" or "closed cell," "high density" or "low density," "half pound" or "2 pound." All of those terms refer to the density of the product, and each is somewhat vague. The density numbers used refer to the weight in pounds per cubic foot of material. The closed cell products typically hold refrigerant gas in their cells, and the open cells hold air. Of course it is the cells that provide the insulation value, just as it is the air trapped between the strands of fiberglass that makes that product work as an insulator.
Closed cell foam at 3-pound density is used in commercial roofing, sprayed on top of the roof, and then covered with a spray-applied membrane. Higher density foams are also used for certain specialized applications.
As you read the materials that brought about fire protection standards for foam, you realize there is some bias on those committees. There are situations where foam is a fire hazard, and there are others where alternate insulation products use dangerous situations to inflate the risk.
One dangerous problem is that the building code allows Class 2 Foam (Flame Spread Rating 75) for use in the building envelope . This material will burn like paper. Avoid it whenever you can, which is always if you work with 2 pound or less density foam inside the building envelope in today's market. The 3-pound density foams used in roofing outside the envelope are usually Class 2 foams. There are some firms that still manufacture Class 2 foam for the building envelope, and that product is less expensive than Class One foam, but it should be specified out by the architects.
Most foam used in residential work is "Class One" foam. This refers to fire and smoke ratings. Class one foam can be open or closed cell. It has a Flame Spread Rating of 25, and a Smoke Developed Rating of <450. Fiberglass products with FS 25 facings are allowed, in some codes, to be exposed to the inside of buildings, especially basements. Some people have construed this to mean that Class One foam can be left exposed. If you take a piece of Class One foam outside and light it with a torch, the fire will go out when you take the torch away. Some people are under the impression that foam will not burn because of that test. In both of these assumptions, THEY ARE WRONG!!! Foam will self- ignite at fairly low temperatures (I have heard 450 °F). The thing to remember is the self ignition temperature is very low.
Foam is very good at holding in heat and stopping air movement. That is why it works so well as insulation. That is also why Class One foam is not safe if it is left exposed in a house. If a fire gets going in a building with foam insulation, the foam will hold the heat and smoke in very well. If the atmosphere in an attic reaches ignition temperature, any exposed foam will self-ignite.
Previously, at least one open cell manufacturer marketed their product as not requiring a thermal barrier or ignition barrier. They have changed that now, and all open cell foams require at least an ignition barrier.
The Spray Polyurethane Foam Association is in the process of getting products tested to get allowances in the code to leave foam exposed in some applications. There is a big difference between insulating a structure from floor to ridge with foam and insulating only parts of the structure with foam. The fire problem is keyed on a complete envelope of foam holding the heat in. If we spray a basement wall, and the rest of the house is conventionally built with fiberglass, and you get a fire in the kitchen, how much risk is there that the basement will get to ignition temperature in under 15 minutes?
Ignition Barrier/Thermal Barrier
The codes that require a covering on foam require a "15 minute thermal barrier." This material is supposed to prevent the foam from reaching ignition temperature for 15 minutes. Half-inch thick gypsum board has been proven to do that, as have coatings like Monocote, which is a spray applied Cementitious product, and some cellulose products like K-13. (R 314.1.2 in the NYS code book, 2007 ed.) There is an exception in the code for "foam plastic insulation" applied in attics and crawl spaces "where there is access only for the service of mechanical devices." Section R314.2.3 in the 2007 NYS code book, 2007 edition, allows for the use of ignition barriers in place of thermal barriers.
There is a list of materials that are approved "ignition barriers" in that section of the code. Among them is 0.016-inch thick steel. The section also allows for the use of alternate products that perform as well as those listed. This has resulted in a market for "ignition barrier paints." These are intumescent products that delay the foam from igniting for a longer period of time than the steel. Some testing has shown those products outlast the steel by tenths of a second. I doubt that the steel holds heat out for very long.
It is odd to me that the code allows this lower grade substitution explicitly for rooms housing mechanical devices, but not for attics or crawl spaces with no access at all. I have my doubts that foam applied in a mechanical room with an ignition barrier is less dangerous with respect to fire than foam in a side attic that is fully enclosed with sheetrock and has no access.
In 2009 International Fireproof Technologies, Inc., came out with a product called DC-315, which is an intumescent coating approved as a thermal barrier on polyurethane foam. It is the only product I know of that can meet the specification as a thermal barrier on foam. The International Code Council has a service called Evaluation Services Reports that tests and certifies this type of product, but the tests are very expensive and they have to be renewed periodically. They are also brand specific, so they test the combination of brand X foam and DC-315. The foam manufacturers have been relabeling DC-315 as their proprietary product to be used in combination with their foam. So now, we have to buy the coating and foam systems that are approved together in the codes to do the job right.
Low-density foam is commonly called half pound or open cell foam. Most SPF product manufacturers make an open cell product now. There are also several soy based open cell foams.
Low-density foam (as a generic product) usually has a flame spread of 25, and a smoke-developed rating of <450. This means it can be called Class One foam. Low-density foam is an effective air barrier and it typically has an R-value of 3.7 per inch. Low-density foam is not a Vapor Diffusion Retarder. It usually has a perm rating of 10 or higher. The low-density foam manufacturers have said the higher perm rating is an advantage because if water penetrates the roof surface, it will migrate through the foam and leave a telltale sign for the occupant. I had one incident where that happened, but it was not as clean as you would imagine. In fact, the foam held water for about 3 years, until one year during the spring thaw the water from the roof was filing garbage cans at a rate of one an hour. The roof was shot. The culprit was a very bad flashing detail, not interior moisture drive.
Low-density foam manufacturers have secured Evaluation Services Reports through the ICC Labs that allow these products to be used with specific brand intumescents and vapor barrier paints to provide vapor and ignition protection. If you have ever tried to conform to a required millage thickness of a coating on a substrate, you will understand why some code officials are not inclined to accept the use of those products when they see the interior face of the open cell foam. It is easy to get a minimum thickness if you apply a coating to a flat glass surface. It is much harder to get a minimum thickness when the surface is irregular.
Low-density foam grows about 100 times liquid volume and cures in a few seconds. This makes it very hard to control the thickness during application. Most people overfill, and then shave off the foam. In that application process, voids in the foam are found and filled as the shaving is done. There is a potential problem in this process because, when the foam rises, it can float wires out beyond the stud faces and hide them inside the foam. Then, the shaver comes around and cuts them off. Foam shavings are usually discarded as construction debris. Some contractors try to put the shavings in an attic and call it loose fill attic insulation, but no one has ever tested that material for R value, so there is no way to know what the R value of the shavings in an attic application will be.
Some applicators are selling the product at an "average depth," which means they are trying to avoid having to shave anything. In that situation, the voids in the foam are not usually found, and the applicator makes out well, but the foam is not going to perform as advertised if it has golf ball-sized holes in it.
The biggest inconsistency with open cell foam is that the samples you see from manufacturers at trade shows are always very fine grained, smooth, soft foam. What you see on the job is not usually like that. It has cells that vary from fine to pea size or larger, and the interior surface is not the monolith you saw in the brochure; it is much more irregular. I had real trouble when we sprayed open cell when I had to set my customers‟ expectations at a level I could deliver.
High-density foam is called closed cell, or 2-pound foam. Most closed cell foam you will find in the building envelope is also flame spread 25, smoke developed 450, but not all of it is.
The refrigerant gives closed cell foam higher R-ratings, commonly R-6.8 per inch. As density of the closed cell increases beyond 2-pound foam, the R per inch decreases slightly. Until 2004, the refrigerant used in closed cell foam was HFC-141b. That gas contributed to ozone depletion and was outlawed by the EPA in 2004. Most foams now have 245FA as the blowing agent. This is sold by Honeywell under the trade name "Enovate".
I have been told that by 2014 there will be a replacement for Enovate that will also have much less Global Warming Potential. If you look at a Life Cycle Analysis of SPF and Global Warming Potential the foam reduces greenhouse gas emissions from building energy use far in excess of the GWP caused by typical offgassing and installation processing. The new blowing agents will improve on this greatly.
All blowing agents presently in use are required by law to be non-ozone depleting.
Closed cell foam adds rigidity to structures. It does not affect compressive strength, and it doesn't do much to enhance resistance to penetration, but it does add racking strength. This resists movement due to wind acting on the structure. This effective insulating material also makes occupants less aware of exterior conditions. The people think it is not as cold as it is outside, and they don't feel as cold inside.
Closed cell foam is an air barrier, and it is a vapor barrier in that it has a perm rating of less than 1 perm at 2 or more inches thick. It is not an acceptable vapor barrier in applications where the vapor drive is one direction all the time, like freezers, kilns, or some tanks.
It is an acceptable vapor diffusion retarder in cathedral ceilings. The Code now allows the use of insulation materials that are less than one perm without roof ventilation in certain circumstances. There really is not an easy way for an observer to check this, but closed cell foam should be applied in layers less than 2 inches thick each. When it is applied too thick, it can shrink or crack because the cell structure is very weak. Cells become irregular and some will be over sized, which will affect R value, air tightness, and perm rating.
Closed cell foam is used occasionally in exterior basement applications. I have not done this, and some literature says insects will use the safety of a tunnel through the foam as an entry path to wood structures, so I discourage it.
There are some 'water blown' foams that are closed cell and have no refrigerant in them. Most are soy based. Water blown closed cell foam has an R value of 5 to 6 per inch. They tend to have slower reaction times, so they drip more during application. The "blowing agent‟ in water blown foam is water, the cells are full of air. I only know one product, and that one has a class one fire rating.
There are both open and closed cell agricultural based foams in the market. These products use products like soy oil or sugar beets as a substitute for the petroleum in the foam. With respect to open and closed cell structures, they perform similarly to any other open or closed cell foam. However, there is another variable here. There are various proportions of agricultural oils and petroleum in these products. All urethane foams are combinations of resin and isocyanate. The isocyanate side of any foam mix is nearly identical to any other foam. That means at least 50% of the foam installed in buildings by agricultural manufacturers is the same as the foam produced for building envelope use for the past 20 years by any foam manufacturer. I recently learned there are "greener" agricultural foams and there are less green agricultural foams. Some foam manufacturers are using both agricultural oils and recycled plastic in their resin; some use agricultural oils and virgin products. I have heard marketing jargon like this: "the resin is 15% soy oil and the rest is recyclables" to "60% renewable resource ingredients on the B side" and ‘there are 2500 recycled water bottles in every drum of resin’.
Unfortunately, I do not know how to stop the spin here. These products do use agricultural oil and recycled content. That is good progress. However, the amount of agricultural oil and the amount of normal polyol is proprietary. How green they are, and which one is most green, is difficult, if not impossible, to determine. The market today encourages manufacturers to get as green as possible. Advances always include failures. When you are on the cutting edge, you occasionally get cut. This facet of the foam industry will grow. Contractors will continue to explore it to satisfy the requests of consumers. My practice is to try new products if we feel they are really going to work, but only to use products in which we find consistency.
We are presently using only an agricultural based, closed cell Class One foam. We have found this product can be applied successfully in about 48 of the 52 weeks of the year. In extreme cold (<10 °F) or extreme heat (>90 °F) it is not really possible to do the work. Yields suffer in intense cold, and the product can froth out of the drum in intense heat. Still, 48 weeks out of 52 is better than most, and I really don't think people want to work when these foams don't work either.
I hope everyone has found this helpful. If you have any questions, feel free to email me, and I will try to answer them.
For details on the restrictions for the use of UFFI (Urea Formaldehyde Foam Insulation) by the U.S. Consumer Product Safety Commission, see:
For information on the residual effects of this material in residences, see the report from Canada Mortgage and Housing Corporation:
Start here to learn about spray foam roofing:
To help understand flame spread rating (ASTM E84 Test) and understand what the numbers mean:
Details about thermal and ignition barriers can be found in the ES Reports that are issued and updated by the ICC Evaluation Services Inc for a specific product. See a typical report here: www.biobased.net/news/icc.pdf
The building department of Duluth, MN, has created a very useful flow chart that you may wish to look at:
**The note on the flow chart about vapor retarders may or may not apply in your climate zone.
Detailed discussion of vapor barriers and vapor retarders:
For additional information about foam in all its forms:
Online videos about spray foam products and other building components are available for free at:
The first resource for anyone interested in applied building science is, of course,
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