A buyer's question, answered from the records
Is spray foam waterproof?
The short answer
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.
Product examples · not ranked
The cans this answer is about
Stanley F903 Black FoamSee it on Amazon 
Kraken Bond Black Foam Waterfall & LandscapeSee it on Amazon 
HandiFoam FR (HFO) II-200 and II-600See it on Amazon 
DAP Wall & Cavity FoamSee it on Amazon
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What the records show
The cans whose makers say something about water
Each line is read from that product’s record, which quotes the maker where the maker’s exact words matter. The last column asks for the one test that would turn the word into a figure.
| Can | What the record says about water | Water absorption test published |
|---|---|---|
| Akfix 805 Gap Filler | Mold-proof, water-proof, over-paintable | None published |
| Sprayman Gaps & Cracks Filler Foam | Moisture and mold resistant, over-paintable | None published |
| Kraken Bond Black Foam Waterfall & Landscape | Contact with water, and "does not harm aquatic or terrestrial life above or below the waterline" (straw sheet) | None published |
| Stanley F903 Black Foam | Waterproof | None published |
| Sprayman Black Foam Sealant | The store says "high-grade waterproof foam ideal for sealing ponds, waterfalls." The sheet lists "Pond, pool and piscine applications." and says "mildew and water resistant" | None published |
| DAP Touch 'n Seal Black Foam Sealant | "Safe for plants and fish" | None published |
What the records show
Where a maker publishes a cell or vapor figure
Closed cell structure and low vapor permeance are what keep water out of foam. These are the products whose makers print either figure, as the record reads it, with the standard where the maker names one.
| Product | Cell structure | Vapor permeance |
|---|---|---|
| DAP Wall & Cavity Foam | Closed cell content above 80 percent (ASTM D6226) | Not published |
| Y'allCanDIY Spray Foam Insulation Kit 6-Pack | Its 80 percent closed-cell statement is a number nobody else in the single-can set publishes | Not published |
| DuPont Froth-Pak 200 Foam System | Not published | 5.4 perm at 1 in and 3.1 perm at 2 in, ASTM E96 |
| DuPont Froth-Pak 630 Foam System | Not published | 5.4 perm at 1 in and 3.1 perm at 2 in, ASTM E96 |
| HandiFoam FR (HFO) II-200 and II-600 | closed-cell content over 90 percent | 0.9 perm at 1 in, which the sheet itself calls a Class II vapor retarder |
| HandiFoam Low Density (open cell) II-250, II-450 and II-1350 | closed-cell content 5 percent | Not published |
Waterproof is a word; water absorption is a test
ASTM D2842 measures how much water a cured foam takes up when it is held under water. It is the figure that would let a buyer compare one can’s water claim with another’s, and none of the 65 product records we hold publishes a water absorption figure. So a can that says waterproof, water-proof or moisture resistant is telling you what the maker believes about it, not how much water it took up in a test.
Closed cell against open cell
The cells in closed cell foam are sealed, which is why it resists water and why it is the kind sold for below-grade and exterior work. Open cell foam is lighter and softer and takes water in. HandiFoam publishes both ends of that range on its own sheets, one closed cell kit and one open cell kit, and the table carries both figures.
Most one-component cans publish no closed-cell figure at all, so which side of the line a can sits on is usually not something its paperwork tells you.
Vapor barrier, vapor retarder
Building codes sort vapor retarders by perm rating: Class I at 0.1 perm or less, Class II above 0.1 and up to 1.0, Class III above 1.0 and up to 10. Closed cell foam at enough thickness can be the vapor retarder in an assembly, and the number that says so is the perm rating the maker publishes at a stated thickness. HandiFoam FR prints one and calls the result a Class II vapor retarder; most cans print none.
Asked next
What people ask after this one
Will spray foam keep water out?
Closed cell foam resists water and seals the gap water would travel through, which is most of what people mean by it. None of the products we track publishes a water absorption figure, so how well a given can does it is the maker’s claim. For standing water or below a waterline, the black pond and landscape foams are the cans sold for that job.
What happens when spray foam gets wet?
Open cell foam takes water in and holds it; closed cell foam sheds most of it. Either way, framing that is wet when it is covered stays wet under the foam, so fix the leak and let the wood dry before spraying.
Is spray foam a vapor barrier?
Closed cell foam can be, at enough thickness, and the perm rating at a stated thickness is the figure that says so: Class II is above 0.1 and up to 1.0 perm, Class III above 1.0 and up to 10. HandiFoam FR publishes its figure and calls it a Class II vapor retarder. Most one-component cans publish no perm figure.
Can you use spray foam outside?
Yes, with a cover. Cured polyurethane foam yellows and breaks down in sunlight, and the sheets in our records that mention sunlight say it discolors or tell you to paint, plaster or coat it. Most of the black foams claim better UV resistance from the color and still recommend a coating; DAP is the exception, saying its black foam will not break down or discolor in sunlight and asking for no cover.
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Where the evidence comes from
- The black pond and landscape foams, in evidence order
- Open cell against closed cell kits
- The two-component systems and what each sheet prints
- Is canned spray foam closed cell?
- Is expanding foam fire rated?
- How much does spray foam insulation cost?
- How long does spray foam take to cure?
- Can you paint spray foam?
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- Every question we answer