Both are spray foam. Both expand. Both insulate. But they behave differently enough that picking the wrong one can mean a soggy rim joist or a wall that cost more than it needed to. The difference comes down to what happens inside the foam as it cures.
The short answer
Closed-cell foam cures into dense, sealed cells. It's rigid, insulates more per inch, resists water absorption and adds stiffness, which makes it the usual pick for rim joists, basements, crawlspaces, metal buildings, garages and anywhere depth is limited or moisture is a factor. Open-cell foam cures into softer, interconnected cells. It's lighter, expands much more, costs less per board foot, absorbs sound well and stays vapor-permeable, which suits deep interior wall cavities and sound control in dry, above-grade spaces.
What the cell structure actually changes
In closed-cell foam, each tiny bubble is fully enclosed and the gas stays trapped inside. That packed structure is what makes the cured foam hard, dense and water-resistant, and it's why the same inch of material holds back more heat.
In open-cell foam, the bubbles break during curing and connect to each other. Air moves between them, so the cured foam is soft and spongy, more like a sponge than a board. It fills space cheaply and dampens sound, but it doesn't bring the density, rigidity or water resistance of closed-cell.
Everything else in this comparison follows from those two structures.
Closed-cell vs. open-cell, side by side
R-value measures resistance to heat flow. The higher the R-value, the greater the insulating power. Always compare R-value at the same thickness.
| What to compare | Closed-cell | Open-cell |
|---|---|---|
| Cured texture | Rigid and dense; trims with a saw or knife | Soft and spongy; compresses under hand pressure |
| R-value per inch | Higher. The closed-cell foams sold on Chem2Go list about R-5.66 per inch; check each product page | Lower, typically around half as much per inch |
| Expansion | Moderate, so it's applied in thin, controlled passes | Much greater, so it fills large cavities with less material |
| Water and moisture | Resists water absorption; at sufficient thickness it also restricts vapor | Absorbs and holds water; stays vapor-permeable |
| Air sealing | Helps air seal as it insulates | Also helps air seal when applied at adequate thickness |
| Sound | Some benefit, but rigidity limits it | Better at absorbing airborne sound |
| Structural effect | Adds rigidity to the assembly it bonds to | Adds essentially none |
| Cost per board foot | Higher | Lower |
| Exterior and below-grade use | Suitable in many applications; check the product documentation | Generally for protected interior use only |
When closed-cell is the right call
- Rim joists, sill plates, basements and crawlspaces, where moisture and condensation are real risks.
- Garages, workshops, pole barns and metal buildings, where the foam bonds directly to metal or masonry.
- Shallow cavities, where you need the most R-value from limited depth.
- RVs, vans, trailers and container builds, where rigidity, low weight gain per inch and moisture resistance all matter.
- Any surface that might see occasional water.
When open-cell makes more sense
We'll say this plainly, even though closed-cell is what we specialize in: open-cell is sometimes the better choice.
- Deep interior wall cavities in dry, above-grade, protected spaces, where its greater expansion fills more volume for less money.
- Interior partition walls for sound control, such as between a bedroom and a living room, or around a home theater or office.
- Assemblies deliberately designed to dry inward, where a vapor-permeable layer is part of the plan.
In those cases, the money saved per board foot buys more coverage than the extra R-value per inch is worth.
A clearer way to decide
Four questions settle most projects:
- Could this surface ever get wet? Rim joists, below-grade walls, crawlspaces, metal buildings with condensation: closed-cell.
- How much depth do you have? Limited depth favors closed-cell, since you get more insulating value per inch. Deep cavities open the door to open-cell.
- Is quiet the goal, or temperature? If you're insulating an interior partition mainly for sound, open-cell is built for that job.
- Is the surface exterior, below grade or exposed? That rules out open-cell in most cases.
Two things that apply to both
Covering. Foam plastic insulation generally has to be separated from occupied spaces by an approved thermal barrier, such as 1/2-inch drywall. Attics, crawlspaces and attached garages can have their own requirements. Check your local building code before you cover anything up.
Application. Both types need clean surfaces, ventilation and the personal protective equipment listed in the product's Safety Data Sheet. Our guide Can You DIY Closed-Cell Spray Foam Insulation? covers preparation, process and the mistakes worth avoiding.
What Chem2Go carries
Our aerosol kits focus on closed-cell foam, because the projects our customers bring us most often, rim joists, garages, workshops, sheds, metal buildings and RVs, are exactly where the density and moisture resistance earn their cost. Compare the brands by how you work:
- IXIRPRO for contractors and serious DIYers, with bulk and pallet options.
- MagicChems complete kits with the gun, cleaner and safety gear included.
- Y'allCanDIY for a first project or a single weekend.
Next: estimate how much you need, or compare spray foam against fiberglass.
Frequently asked questions
Which is better, closed-cell or open-cell spray foam?
Neither is better everywhere. Closed-cell suits moisture-prone, shallow or exposed areas like rim joists, basements, garages and metal buildings. Open-cell suits deep, dry interior cavities and sound control.
How can I tell which type I'm looking at?
Press the cured foam. Closed-cell is rigid and barely gives. Open-cell compresses easily and springs back, like a sponge.
Is open-cell spray foam a vapor barrier?
No. Open-cell foam stays vapor-permeable and absorbs water. Closed-cell restricts vapor movement at sufficient thickness; check the product documentation and your local code for the required thickness in your assembly.
Can I use open-cell foam in a basement or crawlspace?
It's generally not recommended because those spaces see moisture and open-cell foam holds water. Closed-cell is the usual choice below grade.
Is closed-cell foam worth the extra cost?
It depends on the space. Where depth is limited, moisture is possible or the surface is exposed, the higher R-value per inch and water resistance usually justify it. In deep, dry interior cavities, the extra cost buys less.