Open-Cell vs. Closed-Cell Spray Foam: Which Is Right for Your Portland Home?

If you’ve started researching spray foam insulation for your Portland-area home, you’ve probably run into two terms that get thrown around as if everyone already knows the difference: open-cell and closed-cell. They’re both polyurethane spray foams, they both seal air leaks far better than old fiberglass, and they both outperform what’s likely sitting in your attic right now. But they behave very differently once they’re in your walls, your attic, or your crawl space — and choosing the wrong one can cost you comfort and money. Here’s a plain-English breakdown to help you decide.

What Actually Makes Them Different

The names refer to the structure of the foam itself. Open-cell foam has tiny cells that aren’t fully encapsulated, so the finished product is soft, spongy, and lower in density (around 0.5 lb per cubic foot). Closed-cell foam has cells that are completely sealed and packed tightly together, making it rigid, dense (around 2 lb per cubic foot), and much harder. That structural difference drives everything else: how well each one insulates, whether it stops moisture, and what it costs. Open-cell expands dramatically to fill cavities, while closed-cell stays put and adds real structural rigidity to the surfaces it’s applied to.

R-Value and Performance in the Wet Northwest

Closed-cell foam delivers a higher R-value per inch — roughly R-6 to R-7 — compared to open-cell’s R-3.5 to R-3.8. That means in a tight space like a 2×4 wall cavity or a shallow crawl space, closed-cell gets you more insulating power without needing more depth. Closed-cell also acts as its own vapor barrier at about two inches of thickness, which matters enormously in our climate. Portland’s damp winters and humid crawl spaces are tough on insulation, and a material that blocks moisture migration helps protect your framing from rot and mold. Open-cell, by contrast, is vapor-permeable, so it should never be the only thing between a damp crawl space and your floor joists.

Where Each One Shines

Open-cell foam is an excellent, budget-friendly choice for interior applications where moisture isn’t a concern — think attic underside (roof deck) insulation or interior walls where you also want sound dampening. Its softer structure absorbs sound better than dense closed-cell, so it’s popular for media rooms, shared walls, and home offices. Closed-cell is the go-to wherever moisture, limited space, or structural strength matter: crawl spaces, rim joists, basement walls, and any below-grade surface. Many Portland homes end up using both — closed-cell where the house meets the ground, open-cell up in the conditioned attic space. If you’re weighing a full crawl space project, our guide on spray foam insulation walks through how we scope these jobs.

Cost, and What It’s Really Buying You

Closed-cell costs more per square foot — often roughly double open-cell — because it uses more raw material and delivers more performance. But “cheaper” and “better value” aren’t the same thing. In a tight crawl space that floods with humidity every winter, spending less on open-cell can mean redoing the job later when moisture causes problems. In a roomy attic that stays dry, paying extra for closed-cell may be overkill. The right answer depends on the specific cavity, the moisture exposure, and how much depth you have to work with — which is exactly why an in-person assessment beats any online calculator.

One Caution for Older Portland Homes

Spray foam is powerful, but it isn’t automatically the right call for every house. Many of Portland’s charming older homes have knob-and-tube wiring, unusual framing, or ventilation needs that affect whether — and how — foam should be applied. A good installer evaluates these factors first rather than spraying foam everywhere by default. In some homes, a mix of foam at key air-sealing points plus blown-in cellulose in the open attic delivers better results for less money. The goal is a balanced, healthy building envelope, not just the trendiest product.

Not sure which type your home needs? That’s normal — the answer genuinely varies house to house, and it’s the kind of thing that’s easiest to sort out on-site. Forest Fresh Heating & Cooling can inspect your attic and crawl space, explain your options without the pressure, and recommend the foam (or combination) that actually fits your home and budget. Request a free estimate today or call us at (503) 941-6416 to get started.