Spray Foam Insulation Hype vs Reality

Alright my friends welcome back to another episode of the Build Show podcast. That's right my weekly time to get together with you and go deep and I've got a great topic today. We're talking spray foam. I feel like spray foam is a relatively polarizing product in the residential building science world. A lot of building science nerds love it. Some homeowners are frankly terrified of it and the marketing on both sides of the aisle whether you love it or hate it is often wrong. Today I'm going to cut through the noise with some straight talk and what it is, what it isn't and where I would actually use it on a real job. We're going to give you let me show you kind of the outline. We're going to talk open versus close-el. Let's understand what the actual differences are which you might want to use. We're going to answer is it toxic? What are the short and long term risks? I'm going to really honestly try to assess that for you. What are the real benefits of this versus other insulation types? Where is it over hyped? Where is there a gap between the marketing and reality out there? Also is it actually banned in Europe and could that happen in America? Then we'll land on hybrid systems. What's a way that you could use this along with other systems? I'll give you my Matt Reisinger bottom line answer on spray foam. What being said, no sponsors today, nobody has paid me on either side of the insulation aisle here. We're going to be giving you the Matt Reisinger straight talk on spray foam. Let's get going. All right guys, so jumping right in, no sponsors to plug today. I purposely did not want to have a sponsor because I did not want you to think that I've been bought off. I have not been. A little disclosure though, over the, I don't know how many years I've been doing the build job and doing the build show for 18 years. Over that period of time we have had some spray foam sponsors. We have had some non spray foam sponsors. We've had companies that promote it and we've got others that promote the exact opposite of it. So, what I'm trying to do in this podcast is really give you some unbiased advice. First off, open versus close. So, what's the difference in which should you use? Both of these are two component polyurethane sprays. There's an isocyonurate, that's the A side. It's usually an MDI, that's a chemical term, which meets a resin blend or the B side. That's a polyol, P-O-L, Y-O-L, a catalyst, a surfactant and a blowing agent at the guns tip. You know, they spray it with a spray gun and it reacts on contact. If you've ever seen it spray it, it's fascinating, especially open cell because it really blows up and expands. Close cell expands but not nearly as much. The difference in the finish product comes down to cell structure. Close cell foam has tightly packed sealed bubbles, like the core of a surfboard or the inside of a Yeti cooler. Open cell foam has bubbles that actually rupture during expansion, which leaves an open and spongy structure, kind of think of a kitchen sponge. If you've ever been to a closed cell job, rather, you often see some people that have poked a hole in it. They want to test it and see what it looks like. You can easily, on open cell foam, poke your hole straight in, poke your finger straight in and make a hole in that because it is relatively easy to damage. Of course, it's in an area that's inaccessible, so it's not easily damaged, but closed cell is hard to damage. It's rigid. It's closed. It's, like I said, like a surfboard cord. Surfboard cord, sorry. Now let's break it down. Close cell foam. Roughly two pounds per board foot. Often you hear builders or insulators calling it two pound foam. That's kind of a colloquial name for close cell. Our value is roughly our six to our seven per inch, really the highest of any insulation product on the marketplace. So a lot of times people like close cell because of its very, very high R value per inch. Frankly, that's probably why Yeti uses it and they're Yeti Coolers. It's very rigid. It's very dense. It adds real structural and racking strength to a wall assembly. And at an inch to half to two inches roughly, it qualifies as a class two vapor retarder. It's also very, very complete to being a bulk air and bulk water barrier. Meaning we could actually use it on the outside of a house. However, remember though that all foams is very UV resistant. So it needs to be in the dark. You can't just leave it out. It's going to be very much degraded by UV rays. You also could use spray foam, close cell spray foam, as out-solation. I remember seeing Joe Steeberg talk about this 10, 15, 20 years ago showing pictures from the 1980s and 1990s of retrofit houses that got close cell foam on the outside of the house. Let's say a historic house that you didn't want to insulate on the inside, but you could change the outside of the house. People were using it on the outside decades ago. In modern times, you've seen this on the build show live, 2026 house. The house we did up in Dallas, gosh, I'm totally blanking on the builder's name, but he used insofast X brackets on the outside of the sheathing. I think it was zip system sheathing. Sprayed a couple inches of close cell foam and then he had full out-solation on the outside. Very interesting use case for it. Very best for roof decks, rim joists, basements, anything that's below grade or possibly flood prone because it could be dried out. It's not going to absorb water. Anywhere where cavity depth is limited and when you'd maximum our value per inch, it's also been the de facto spray foam for cold climates. You don't see anybody in Boston spraying almost any open cell. It's pretty much always close cell. If you're in a cold climate, this is your choice. Remember though that it's at least double if not more the cost of open cell. In the south, you're going to find more open cell by a wide margin and then close cell. Let's talk about open cell. Density roughly half pound per board foot. That's a foot cubed basically. Mount and spongy are values vary from about 3.5 to 3.8 per inch. It expands fast and fills deep cavities in a single pass. Often you can spray three inches in a single lift which is going to keep labor and material cost down. This is vapor open. It is not act as a vapor retarder on its own. So an assembly being used with open cell needs a deliberate vapor control strategy. We need to think about how to control vapor flow. Fast fit. Full depth interior walls and exterior walls. Add it cavities two by six deeper. Actually let me eliminate what I just said. I wouldn't use this on interior walls. I would say interior cavities of exterior walls. Let's be more specific. Typically two by four, two by six type exterior walls. Places where budget matters where we're not worried about the vapor profile. That's why it's often used in the south. As well as being used a lot in the south to form condition attics. Spray foam both flavors open and closed. Stick to the substrate. So I could spray it on that roof deck and it's going to stick on that roof deck. It's been a really easy way for me and a lot of builders to move from traditional buildings that have attic insulation on the flat and unfortunately ducks above those attics. So now spray foaming and moving that insulation layer to the rigid or to the exterior of the building forming a conditioned attic space. And again because open cell is relatively cost effective compared to closed cell, it's used a lot in the south. Now here's a rule of thumb for you. Use closed cell where you need moisture or vapor control, structural rigidity or maximum R value in a thin cavity. Work decks, rim joys, foundations, that sort of thing. Open cell where you have full cavity depth, budget is a bigger factor and vapor management is handled elsewhere in the assembly. Woo, we're nine minutes in and I've only gotten through one of my pages. I've got a lot of notes for this one. Climate zone changes the vapor control answer. In other words, this isn't a one size fits all. If you're listening to this in Minnesota, I'm going to have a different answer for you on spray foam than if you're listening to this in Florida. So let's keep that in mind. Next up, let's talk about is it toxic? When I think about toxicity, I want to break this down into short term and long term. Where the real risk lives for spray foam is installation, not a long term cured product. Potia data shows installer inhalation exposure during spraying routinely exceeds occupational exposure limits. That's why license then dollars wear supplied air respirators and full protective suits. That's a real and documented occupational hazard and repeated occupational exposure to I so sorry. can cause sensitization. Asma-like reactions, and this is overwhelmingly an installer occupational issue, not a homeowner after it has cured issue. That's why you see my buddy, for instance, Travis Brungard. He's a big detractor of spray foam, not because he thinks there's a problem for homeowners because he doesn't like seeing installers exposed to it. So keep that in mind. I think that, and I would make the esthetic here, that the real risk of spray foam is massively with the installer, not with the finished product. Properly mixed, properly cured spray foam is chemically stable within the manufacturer's stated re-occupancy window, which is pretty common to say 24 hours. But of course, you're going to have to verify that with your specific chemical set, with your specific manufacturer. The real short term danger is off ratio mixing. If the A side and the B side, there's two hoses that come into that gun. If the ratio is off and isn't blended correctly, that could be because of bad equipment, bad training, or the wrong temperature. The foam can remain chemically uncured for weeks or months or longer. That's where you're going to come into a house and have a persistent odor. Sometimes the foam is going to be sticky your soft. You might get headaches or eye or respiratory irritation. In really bad cases, people have had to actually vacate and have the foam removed. I have one story that I know of like that. In Austin, Texas, almost 20 years ago, I was interviewing for a custom home. The customer told me they were very chemically sensitive. And I sense that they were going to be, frankly, a difficult client. She did not hire me. She hired a different builder. And the spray film contractor did the job was a good one. Spraying a brand name that we all would recognize, they sprayed that and it smelled afterwards. Not just for 24 hours, but continued to smell weeks and months afterwards. They stopped the job. Homeowner sued the builder. Homeowner sued the manufacturer. That's the only time I've ever really heard of this happening. And I think it's ironic, not ironic, not funny, but terrible that it happened to somebody that said they were chemically sensitive. I would put a pin in that. I'm going to come back to that. But I kind of got an inside story from a spray film manufacturer. Years ago about that, I relayed the story. And he said, you know, probably what happened, Matt? The price of one of the very expensive chemicals and the multiple chemicals that goes into that drum of spray foam. One of those chemicals is dang expensive, like by the gallon, crazy expensive. And I suspect that chemical spiked in price, the manufacturer substituted that chemical for a different one. And that chemical that they used had a really bad fish smell. And ultimately, I think that this guy was telling me, they probably got a slightly bad ratio mix in the gun. The installer didn't do a good job. And you've got a fish smell that persisted. The spray foam wasn't spongy. It wasn't bad. It seemed like it looked good. If you didn't have it in the nostril, you wouldn't know there's a problem. But every time you walked in the house, it had that fish smell. So this is not a zero risk product. But I would tell you that I've been spraying foam for 20 years. I've never had that happen. And I've seen probably thousands of spray foam jobs in my town. And I only know of one that's gone bad. So I think one of the reasons why I wanted to make this podcast is if you get on the interwebs and look, I swear there's some fake news channel style that has a story about spray foam nightmares that keeps getting played over and over. And there are people that are extreme detractors of it. I'm a very middle ground guy. I would vote independent on this. If there's a right side and a left side of the aisle, I feel like I try to be an independent thinker in all that I do. And when it comes to spray foam, the majority of the risk is with the installer. They've got to take their PPE seriously. The risk for the homeowner is extremely limited or extremely low after the foam has cured. When they move in weeks or months later, or maybe a week later, if this is a remodeled job, let's say, there's very, very little chance of there being a problem. That chance is not zero. Don't get me wrong. Don't hear me mistakenly. But it's very low. Once the foam is cured and reacted, spray foam is generally considered chemically stable and inert. Documented long term complaint cases trace back almost entirely to installation error, not the finished material itself. The EPA is flagged that long term exposure data still has gaps and recommends extra caution for sensitive occupants. And this is my kind of research on the inner webs. People that have asthma, chemical sensitivities, or maybe infants of the home in the home are people that should generally think about avoiding spray foam. Practical risk mitigation talking points for listeners. Higher and experienced certified installer, ask about their ratio, monitoring, and quality control process. Make sure the substrate and ambient temperature requirements are met. In other words, don't spray your spray foam when it's too cold. Winter time is really where things go wrong because it's too cold of a substrate. That doesn't happen as often in the south, but if you're in northern climates, that can be a problem. Fall of the manufacturer stated reoccupancy time. Don't just gas. Don't just move right in a couple hours later. And if you're worried about it, there are third party air quality testing available. And as a side note on that, I did a video that was a sponsored video years ago by a company called Natural Polymers. They have now been acquired by Owens Corning. And they came out with a product, I'm not quite sure how long ago now, it's called a decade ago, that had very, very low smell, very low VOCs, that's volatile organic compounds. Both for the sprayer and also that smell went away extremely quickly. Like you could walk into the house an hour after they're done spraying it, and there was no smell. They sent a guy out to the job to take VOC measurements at time of install at 10 minutes after, 30 minutes after the next day, and the numbers were off the charts low. I suspect there's probably other products out there in the marketplace now like that, but that is one product that I really like. And for friends and family that are asking me about spray foam, I always say, hey, that's one that I really trust. There probably are some others out there, but Natural Polymers by Owens Corning, I really like that product. I do want to take one quick second to talk about canned foam or two-part foam. When you buy canned foam at the store, you know, that, I don't want to say the names, but you know that, that can of one-part foam, the part A and part B are in that foam, and that is closed cell foam in the can. That's not the same as a guy with a rig doing a serious spray foam insulation job. And the DIY kits that is a part A part B, I've used those before. I've had very mixed success with those. I even had the rep do one of those in my job one time, and it didn't turn out right, and it was like a trained rep doing it. So don't be fooled by the hype on these, you know, $400, $500 kits. They're not easy to use, I don't love them. Frankly, canned foam is better if you're going to do a small insulation job sometimes than the part A part B, because those are relatively difficult to get correct. Now let's talk about spray foam versus other insulation types. Here's where spray foam wins. Air ceiling. Close cell into a lesser extent open cell does form both insulation and air barrier in a single pass. Fiberglass, blown cellulose, mineral wool, they do nothing for air ceiling, they're in effect a furnace filter. So they're not going to help your building when it comes to its air ceiling. They need a separate air control layer. Now this can be oversold in terms of how much that air ceiling helps, but it definitely does help. And let me back up a minute and tell you a story on this. When I did my very first custom home here in Austin, Texas, it was when I moved here in gosh, 21 years ago now. I did open cell foam in the entire envelope of that house because I really felt like gosh, I'm going to get a very tight envelope by doing spray foam everywhere. I did it in the roofline, I did it in the walls, the band joists, not below grade, but it had some like walk out basement type walls where I did it. And I think my blow order score in that house was around a two to 2.2 something like that, ACH50, which is good. I met code for sure, but it was nowhere near what I was hoping for, which would have been below one ACH50. Ever since then, I started doing all kinds of cocks and sealants on the inside, different types of spray foam, even closed cell spray foam with varying levels of success. But I've come to realize, or I've realized this now for a while, you've seen it, that house wrap on the outside with spray foam on the inside isn't the panacea that we all thought it was going to be. It's good, don't get me wrong, but it doesn't solve all our problems with our houses. It solves a huge problem, which is why I'm going to be doing this. which is ducks out of the condition space, but it's not as good of an air seal as what we'd really like for our houses for best practices. So you'll see me on all my houses today, abandoning traditional staple on house wraps and going with either zip system sheathing, which is basically a pre-fluid applied from the factory, true fluid applied, like Prostikos our guard system or polygards blue barrier system, or peel and sticks. I use a lot of polygards UV2-40, but I've also used a bunch of others that were vapor open as well. And those work great too, especially if you're in a northern climate, like Henry's peel and stick or Delta's peel and stick, there's a bunch of good ones out there. Here's where spray foam wins though. The density of close cell in that high R value per inch at R six or seven per inch, if I have four inches, that's almost R 25, or could be higher than R 25 with only four inches. So for instance, in my personal build, I had this one roof line on a pop-up. I have some windows in my staircase that let some light in. I've a really short roof that I framed with two by fours. How else was I gonna insulate that on the inside? I had four inches of poly iso on the outside, which was R 25. A lot, but not enough to get me to code insulation, I ended up using a close cell spray foam on the inside. So that roof line is a nominal R 50. It's not really R 50, 'cause I've got some thermal bridging there, but I've got R 24 or 25 of Atlas poly iso on the rooftop. And then I've got four inches of close cell spray foam on the inside, or actually three and a half, I guess, technically. So that's where it really wins. The other place I use close cell at my house was on my band Joyce area. Anywhere you've got platform framing, where you've got Joyce that's sit on top of a wall. That Joyce space on the outside is really hard to insulate with traditional bad insulation or with blown in insulation. I like to spray foam that band Joyce. It adds a little bit of air tightness, and it sticks. So I've got good insulation where it sticks. And I really like that. I also used it in my garage. If you were to walk into my garage during the framing stage, if you looked up, you'd see a van tech decking, and that was my boys bedroom above my garage. And if you were to look towards the house, you'd see a bunch of blocking, some basically OSB that I put in to block my eye Joyce, which rain continuous from the garage ceiling into the kitchen ceiling. That was my second floor framing. I blocked that with solid blocking, but then all my trades drilled through that. I made sure I had to tell them one hole for one thing. So I've got a plumbing pipe. I've got multiple holes for one thing of Ro-Mex wiring. And where those penetrated close cell spray foam was really the best choice for me in terms of getting a good air seal, keeping those fumes from the garage out of the house, and also insulating the house from the garage's heat and cold. So those are some great places. But the majority of my house, I used Rockwell standard cavity insulation. I'm monopoly framed in my house. I taped at the outside between my roof and my wall sheathing. So I've got good tape joints. And so I wasn't using the spray foam in any of my walls or roof line for air sealing, or frankly for insulation, especially because I purposely made the roof geometry so that I could frame it with two by eights and fit a standard bat in there. And then I've got exterior rooftop insulation. So my roof line is around our 60 year so, which should work in really just about any climate zone in America. The other thing I want to talk about here when it comes to the risk of spray foam is, I think those people that are demonizing spray foam forget that really bulk water is the biggest problem for our house and not the risk of getting a bad spray foam job. You've got to spend your time on bulk water people. We've got to have good overhangs. We've got to install our windows properly. We've got to seal our penetrations from a water perspective properly. And then when you've done all those, like I did at my house, then you can go, okay, I'm going to eliminate or greatly limit the amount of spray foam I'm going to do in my house, which I did. And I'm really happy with that. I love it. I'm going to give you a couple of pieces of advice. First off, here's a more alternatives to spray foam make sense. If you were cost sensitive spray foam, typically is more expensive than other insulation types. And we don't have to rely on it, especially when we do monopoly framing. The other thing I don't like about spray foam is it's very hard to reverse a spray foam insulation job. (laughs) It sticks in the cavity. Any builder listening to me who's ever tried to peel out a cavity of insulation, so the plumber could put a pipe in or the electrician could wire it, knows that it sucks getting out of that cavity. I would not want to remodel a house where I had to demo a full wall of closed cell spray foam and remove it without damaging the sheathing or the framing or the wiring behind the walls, whatever. It's really hard. It's basically a permanent bond. And it's extremely hard and frankly, extremely expensive to remove. So if you're thinking about remodelability, which I was in my house, I don't love it for remodelability purposes. It's going to suck for that next builder remodel or down the way. I also would absolutely not use it if you have any chemical sensitivity. Not because I think it's a problem, but because I'm worried about you thinking it could be a problem, right? If you're worried about it in any way, shape, or form, just don't do it. There's plenty of alternatives out there. So if you're worried about it, don't do it. If you have it already, like I do at my house, I don't think about it. I don't worry about it. It's fine. I've got no problems. The other thing you remember is mineral wool specifically brings much better fire resistance and acoustic performance than spray foam. This is where I'm going to wrap up. You know what actually guys? I'm going to go to a part two, which is like spray foam myths because I got a bunch of good things here that I don't want to forget. And I just don't have time to do this. So with that being said, let's wrap this up on under 30 minutes. I'll do a part two on this spray foam topic. Hopefully you've learned something. This is basically a webinar with Matt Reising or thoughts on insulation. I appreciate the support guys. I'm sure you've been inundated with it, but remember, Build Show Live is coming up in San Antonio, September 10th through the 12th. If you're listening to this after September 12th of 2026, we'll have another show next year in Houston. Dates will be announced any moment. But stay tuned for part two of spray foam. We're going to go through some of the myths about spray foam, both good and bad myths. We're going to talk about, is it banned in Europe? Could that happen in America? And we're going to talk about some hybrid assemblies. Gosh, I totally misjudged how long it would take me to get through this material. And if you've listened to my podcast for any length of time, I don't like going super long. I like to go under 30 minutes. Let me say guys, follow us on Facebook or Instagram. I'll see you at Build Show Live. And we'll see you next time on the Build Show podcast.