Frequently Asked Questions:


What is spray foam? How does it work?

Spray polyurethane foam (SPF) is a spray-applied plastic that forms a continuous insulation and air-sealing barrier on walls, ceilings, roof decks – any surface, really. SPF insulation is an excellent thermal insulator and stops air leaks through cracks, seams, and joints dead in their tracks.

It is made by heating, mixing, and reacting two liquid components (iso and resin) at the job site to create foam. The liquids react quickly when mixed, expanding on contact to create foam.

Spray foam is a relatively new technology, right?

Nope. We've been spraying it since 1975. Closed cell foam first entered the mainstream back in the 60s; open cell hasn't been around as long – it marks its beginnings in the early 90s, mainly as a cheaper alternative to closed cell. We explain the difference between open and closed cell on other pages on this website.

What does it cost per square foot?

While internally, we calculate the cost of your project primarily using the square footage of the area we are going to insulate, we do not give out that information. Every job is different. Some may require hours of prep work, some will require much more clean-up than others, and some are just more cumbersome to spray and will command higher rates (i.e., crawlspaces and attics). What you're looking for is the total job cost – that's what we'll provide.

OK, I understand. But can't you give me a ballpark idea of what to expect?

One inch of closed cell insulation starts at around $1.80 per square foot, 2" around $2.70/ per square foot, and so on. The first 1" has the most associated cost. If you upgrade to 2" or 3", it does not double or triple the price. For open cell insulation, 3" starts at around $1.60. per square foot, 5" around $1.95 per square foot, and so on. Again, the first 1" is the most expensive. Keep in mind that closed-cell spray foam has twice the R-value of open cell per inch. Learn more about the differences between the two types of foam here: Open cell or Closed cell

Is spray foam more or less expensive than other types of insulation?

Expensive is a relative term; if comparing up-front costs to the baseline, fiberglass, then, yes, foam is more costly. It will cost roughly 3-4 times more to insulate your house with foam than fiberglass.

That seems like quite a bit. Is it worth it?

Case studies comparing identical or similar houses insulated with foam vs. fiberglass across the US indicate potential monthly savings of up to 48% - see these documents for more details:

Henry case studies

Roanoke, VA (case study #2 from Henry brochure)

Rutledge, GA (case study #3 from Henry brochure)

Denton County, TX - Habitat for Humanity case study

As a general rule of thumb, you can expect a 4-6 year payoff in using foam over fiberglass. This payoff will vary depending on what you pay for gas and electric in your area. We know that budgeting more for insulation in a new house or remodel project isn't as fun as, say, upgrading the kitchen but remember: it is one of the few items that will continue to pay you back, year after year, over the life of the house, long after your new kitchen has become outdated and the family room carpet has been replaced. You'll only do it once. Do it right.

Open cell vs. closed cell – what's the difference?

Both can give an air-tight seal, and both will insulate well. But there are still many differences – see our pages about this topic here: Open Cell Insulation or Closed Cell Insulation

How does spray foam compare in R-value to fiberglass batts or cellulose?

Fiberglass, cellulose, and open-cell foam have R-values of approximately R-3.5 per inch. Closed cell is figured at R-7 per inch. These values will vary slightly depending on the specific foam brand, but for all practical purposes, using R-values of R-3.5 and R-7 are close enough.

The US Dept. of Energy has an informative page on different types of insulation: http://energy.gov/energysaver/articles/types-insulation

The quote you sent me says spray walls w/ 2" closed cell R28 fiberglass equivalent. Isn't that off by a factor of 2?

Good eye. Most people are comparing our spray foam quote to their fiberglass figures. We feel it makes a better comparison to double the lab-based R-value of foam to give its real-world R-value when held side-by-side with fiberglass. However, it is still an apples-oranges comparison. Because of foam's air-sealing qualities, 1" of closed-cell foam will outperform 10" of fiberglass even though their lab-based R-values are vastly different.

For the long answer, see the next question


So technically, an R-21 fiberglass batt has the same insulating value as 3" of closed cell foam since they both have the same "prescriptive" R-values, right?

That would make the most sense, right? But it couldn't be farther from the truth. The tests to determine R-values printed on a package of insulation are performed inside a lab with no wind and controlled humidity. And how many houses are built inside a lab? Exactly. In the real world, there's wind. And moisture. And myriad unsealed joints and cracks. And it's in these conditions that fiberglass must provide an insulating value of R-21. Go ahead and Google "fiberglass furnace filters" and look at the results. That's right: the same product used to filter moving air is also supposed to insulate your home and stop the wind. We could go on and on about the pitfalls of fiberglass insulation, but the following article does a great job of explaining the 'R-value myth':

R-value myths (excerpt from Urethane Foam: Magic Material - And the Best Kept Insulation Secret by David South)


If closed cell spray foam has an R-7 per inch, why has another contractor told me that 2" of closed cell equals an R-21?

We've recently heard this on at least two occasions: another insulation contractor explained that their closed cell foam provides an R-7 with 1", but somehow, amazingly, it also provides an R-21 by merely bumping up to 2"! Either they are using a complicated math formula for computing R-values that we are not privy to, or they are stretching the truth (we'd guess the latter). Most likely, they are trying to convey how much more effective spray foam is compared to fiberglass (it is) and are mixing "prescriptive" (lab-based) and "effective" (real-world) R-values without explaining the difference. (See the previous two questions for more detail.)


So, how can I tell exactly what the R-values are for a given foam brand rather than through some insulation contractors?

Go straight to the source! Most foam companies (if not all) make the technical and product data sheets for their foam products publicly available on their websites. Just ask the contractor which brand of foam he uses, then Google it. If his claims don't match up with the manufacturer's specs, call him out on it. Here are a few links to the product information of some of the more prominent foam manufacturers (these are for their closed-cell products):

  • Demilec (Heatlok Soy 200) (PDF)
  • SWD QS118 (PDF)
  • BASF (Spraytite 178) (PDF)


Won't spray foam make my house too tight? My contractor/friend/neighbor tells me houses need to breathe.

The proper mantra is this: Build tight, ventilate right. From an energy conservation standpoint, the last thing you want is a drafty house. Repeat after me: air seal, air seal, air seal. You want your home as tight as possible. Your goal is lower energy bills, right? And unfortunately, even if you foam from the peak of the attic to the basement floor, you will still have leaky doors and windows.

You will need to actively manage a couple of things once you have a tight, energy-efficient home: humidity and fresh air. Winter typically means running a humidifier to fight against skin-drying, static-zapping dry air. However, with a foamed house, the moisture from all your cooking, hot showers, and even breathing can raise the humidity indoors enough to require a dehumidifier to lower the moisture. This humidity happens because your house no longer leaks all that air out! Stale air can also become a problem, but that can be easily fixed with an air-to-air heat exchanger. These devices draw fresh air from the outside and expel the stale air. In the process, exchangers transfer the heat from the warm, outgoing air to the cool, incoming air (and vice-versa in the summer). These units are ERVs or HRVs; contact your HVAC contractor for more information.

Again, remember: Build tight, ventilate right. Houses don't have lungs.


One of your competitors tells me their foam is better than everyone else's. So I'm sure yours is "better than everyone else's, too," right?



Wait, you said no?

That's right. Our foam is not better than theirs, and theirs is not better than ours. As much as some installers would like to tell you otherwise, foam is foam. For all practical insulation purposes, all open-cell products are the same, as are all closed cell. There are higher-density closed-cell foams for roofing applications – but we're talking interior insulation in this situation. Yes, there are many different brands of raw materials, and some insulation companies will prefer to spray one over the other for various technical reasons. Still, for our customers, our closed cell performs like their closed cell, and our open cell acts just like their open cell.


So if all foams are the same, why would I choose your company?

The same way you would decide with any other trade: years of experience (we've been spraying foam since 1975), quality of workmanship, knowledge level of the sales reps, job site professionalism, having proper liability/work comp insurance, and finally, price.


What can you tell me about the flash and batt system I've heard about?

While we usually don't recommend it, it is a legitimate insulation technique when done correctly! But in our opinion, it's not worth the small amount of savings you might gain. The basic premise is this: we spray a layer of foam no less than 1", then install a fiberglass batt over the top. You get the best of both worlds – a tight air seal and cheap R-value from the fiberglass. Here's the first problem to overcome: this system requires 2x6 framing to allow room for the foam, and a 3 ½" batt – 2x4 walls will NOT work with this system. The primary concern deals with proper installation. The foam must be sprayed no less than 1" thick, even in the low spots (all thicknesses quoted are technically averages, but should vary less than ¼" from specified thickness). Any less than 1" and the foam could have cold spots, resulting in potential condensation in your walls, which leads to mold and rot. (Remember: warm, inside air will pass through the fiberglass and condense on the cold foam.) It is also possible that some unscrupulous contractors may spray much less than 1" of foam, then quickly cover it up with fiberglass, and you, the homeowner, are none the wiser. (We only mention this because we have witnessed this ourselves.)


Is spray foam flammable?

The foam we use (whether open or closed) contains fire retardant and is rated "Class I" or "Class A," meaning it has a "flame spread" rating of 25 or less – lower is better. Our foam will burn if you hold a torch to it, but once the flame is removed, it will quickly go out. THIS DOES NOT MEAN OUR FOAM IS FIREPROOF! It does indicate that it is not match-light, nor will a few stray sparks ignite it. If you have a house fire, the foam will burn. Do not expect it to do otherwise. Building codes usually require all foam to be covered with a thermal barrier – in a typical home; this will be drywall. In unfinished areas (basements, crawlspaces, attics), we have a code-approved white thermal barrier coating that we can spray over our foam to meet code requirements.

Does spray foam off-gas? Does it need to cure before drywalling?

No - unless it was improperly installed, primarily if the ratio of the two components mixed while spraying was not kept at a 50-50 ratio. While the foam is being sprayed, fumes are generated from the heat and the chemical reaction. This is why we wear respirators and will try to keep the job site ventilated (when possible). Once we finish spraying, there are no more fumes generated. Sometimes it can take a few hours to remove the lingering fumes, esp. if the work was done in a crawlspace or basement with few windows to ventilate. But generally, the smell is gone within a day or so. You can start hanging drywall as soon as we leave – there's no need to wait days or weeks first.