Spray foam questions by category
Each category’s questions in one place: the question pages filed under it and the questions buyers ask about it, answered from the makers’ documents and the product records. Pick a category, or ask your own at the bottom of the page.
Questions about any spray foam
- Is spray foam waterproof? Water resistant, mostly, and the word waterproof on a can is the maker’s word rather than a measured result: none of the 65 product records we hold publishes a water absorption figure. What keeps water out of foam is closed cell structure and low vapor permeance, and 6 of the products we track publish either figure. 4 of the 6 cans that say anything about water are black pond and landscape foams, sold to sit in it. Read the answer
- How long does spray foam take to cure? On their own sheets, the one-component spray foam kits we track are tack-free in 3 to 10 minutes, ready to trim in about 40 minutes, and 4 of the 5 put a full cure at 24 hours. Two-component kits set far faster, tack-free in 15 seconds to 3 minutes. On re-entry, none of the 5 one-component kits publishes a time for going back in, while 3 two-component makers give 1 hour with ventilation. Read the answer
- Can you paint spray foam? Yes, once it has cured. Of the 47 spray foams whose makers say anything about it in our records, 35 call the cured foam paintable and the other 12 tell you to paint, plaster or coat it where it is left in sunlight. Wait for the full cure, which 4 of the 5 ranked kit sheets put at 24 hours. None of the documents names a type of paint. Read the answer
- Is spray foam heat resistant? Up to about 240 F once it has cured, and no maker in our records claims more. The FastCoat, ThermCoat, SuperCoat and SprayCoat sheets all print -103 to +239 F, the two-component makers stop at 240 F, and the fire block foams top out between 194 and 240 F, no higher than the gap fillers. That is a service temperature, not a fire rating: DuPont, HandiFoam and Loctite warn that cured foam can burn, and DuPont and Loctite keep it away from heaters, chimneys and other hot surfaces. Read the answer
- Is spray foam insulation safe? Safe to use the way the label says, and not otherwise. All 17 spray foam safety data sheets we could read class the foam in the can as a respiratory and skin sensitizer, which may cause allergy or asthma symptoms if inhaled, because it carries MDI isocyanate, and 13 of them add suspected of causing cancer. Those classes describe the product in the can and while it is sprayed; of the documents we read, only HandiFoam’s say the cured foam is non-toxic and inert. None of the one-component kit makers gives a time for going back into the room, while DuPont and HandiFoam give 1 hour with ventilation. Read the answer
- How do you get spray foam off your hands? Wash it off at once, before it cures. The safety data sheet of every one of the 24 products in the table tells you to wash or flush the skin with water, and 14 name soap. DuPont’s 5 Great Stuff sheets add that cleaning very soon matters and that a polyglycol-based skin cleanser or corn oil may work better than soap and water. None tells you to put acetone on your skin: the one sheet that names acetone, DAP’s, names it for clothing and other surfaces, and says cured foam comes off skin by persistent washing with soap and water. Read the answer
Spray foam insulation kits
Open the category- Is canned spray foam closed cell? Mostly by name rather than by number. 10 of the 56 canned products we track are called closed cell somewhere in our records, and for 4 of them the words come from a retailer’s listing title. 2 publish a closed-cell content figure, the percentage of cells that are sealed, which is what makes the claim checkable. The two-component kits state their cell type on the sheet, and 1 of the 6 closed-cell systems prints the percentage. Read the answer
- How much does spray foam insulation cost? For the foam alone, a one-component 24-can kit claiming 480 board feet cost $314.99 to $389.95 across the 7 we could price in stock, which is $0.66 to $0.81 per claimed board foot. A board foot is one square foot at one inch thick, so 1,000 square feet at 1 inch is 3 kits at the makers’ claims, $944.97 to $1,169.85, before any allowance for waste. Read the answer
- Is spray foam made in the USA? 5 of the 14 spray foam kits we track describe their seller as American owned, family-owned or US-based on its store or its listing, and none of those 5 says where its foam is made. 3 of the 14 do say where the foam is made or who makes it. Owning a company and making a product are different statements: the FTC holds an unqualified Made in USA claim to the product being "all or virtually all" made in the U.S., and it reads a label by "the overall impression" it gives. Read the answer
Asked by buyers, answered on the category page
- Is a one-component spray foam kit as good as a two-part kit?
- Do I need a vapor barrier over one-component spray foam?
- Will one-component spray foam stick to metal, and will a pole barn, container or van sweat behind it?
- Can I stop halfway through a spray foam kit and finish the next day?
- How long do unopened spray foam kit cans last, and how should I store them?
- Can I spray a one-component foam kit on the underside of my attic roof deck?
Two-component kits
Open the categoryAsked by buyers, answered on the category page
- Froth-Pak 200, 620, 630 or 650: which one do I need?
- Can I stop a Froth-Pak kit and use the rest later, and does it expire?
- How warm do two-component spray foam tanks need to be, and how do I warm them?
- Why is my two-part spray foam soft, sticky, shrinking or coming out like popcorn?
- Froth-Pak or Handi-Foam: how do the kits compare, and is either one a vapor barrier?
- Can I leave two-part spray foam uncovered on a rim joist, in a crawl space or on a basement wall?
Gap and crack foam
Open the categoryAsked by buyers, answered on the category page
- Can I use expanding foam under a bathtub or shower base to support it?
- Can I reuse a half-used can of gap filler, and how long does an unopened can last?
- Can I use gap filler foam around hot water or radiator pipes?
- How much gap will one can of gap filler fill?
- How wide a gap can a gaps and cracks foam fill before I need a big gap foam?
- What will expanding foam not stick to?
Window and door foam
Open the categoryAsked by buyers, answered on the category page
- Should I use spray foam around a new window, and does the window maker allow it?
- How do I foam around a door jamb without pinching the door?
- Can window and door foam go on the outside of a window where the sun hits it?
- How soon can I trim window foam and put the casing on?
- How do I remove excess window foam without damaging the frame?
- How cold is too cold for window and door foam?
Fire block foam
Open the categoryAsked by buyers, answered on the category page
- Can I use fire block foam around electrical wires, outlet boxes and low-voltage cable?
- Will an inspector accept fire block foam as fireblocking?
- Which holes actually need fire block foam?
- Can I use fire block foam as ordinary gap filler or insulation, for example around a window?
- How much does fire block foam expand?
- Can I use fire block foam around PVC, CPVC or ABS pipes?
Pest block foam
Open the categoryAsked by buyers, answered on the category page
- Can I use pest block foam next to a baseboard heater, radiator or hot water pipe?
- Is it safe to spray pest block foam behind a stove or around a gas line?
- Can I use pest block foam around electrical wires, outlets or conduit?
- Should I stuff steel wool or copper mesh into the hole before I foam it?
- Does pest block foam keep out ants, roaches, wasps and other insects?
- What is the difference between pest block foam and regular expanding foam?
Black pond and landscape foam
Open the categoryAsked by buyers, answered on the category page
- Is black pond foam safe for reptiles, frogs and vivariums?
- Can I use regular Great Stuff Gaps & Cracks, or another black foam, instead of Great Stuff Pond & Stone?
- Does pond foam need to be sealed with silicone before water or animals touch it?
- How long after foaming can I run the waterfall or put the animals back?
- Will waterfall foam hold rocks in place or glue stones to a pond liner?
- Does black foam stick to glass or wet stone?
Wide spray foam cans
Open the categoryAsked by buyers, answered on the category page
- Can I insulate a whole wall, or fill a closed wall cavity, with wide spray cans?
- How many square feet does one wide spray can cover?
- Why did my wide spray foam come out thin or not expand?
- Can I spray wide spray foam overhead on a ceiling?
- How thick can I spray wide spray foam in one pass, and when can I add another layer?
- Will wide spray foam stick to metal, like a garage door, shed or van?
Foam guns, cleaners and nozzles
Open the categoryAsked by buyers, answered on the category page
- Are spray foam guns universal? Will any gun-grade can fit my gun?
- My spray foam gun is clogged or stopped spraying. How do I fix it?
- Can I leave the can on the foam gun between jobs, and for how long?
- Can I clean a foam gun with acetone instead of foam gun cleaner?
- Can I reuse a spray foam straw or nozzle, or do I need a new one each time?
- Can I put a longer barrel or extension on a spray foam gun?
Ask the research desk
A question these pages do not answer yet? Send it to the desk. Questions are answered from the same records as every page here, the makers’ documents and the listings, and are not published as they are sent.
When the records can answer one, it becomes a question page with a dated note that a reader asked it. Your name and address are never published. We cannot answer every question, and we cannot judge one house we have not seen.
From the job to the finished wall
Plan the job in five questions
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Where are you insulating?
A garage ceiling, a rim joist and a van wall each ask for a different foam, thickness and cover. Start with the job.
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What will it cost?
Board feet are the area times the thickness. Price the kits that cover them against hiring the job out.
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What do you need?
A kit, the gun and cleaner it works with, something to cover what stays clean, and the gear you wear.
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How do you do it?
Check the temperature, prepare the surface, spray in passes and cover the foam where people live.
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How long does it take?
The sheets give a tack-free time in minutes and a full cure in hours; only some say when people can go back in.