Spray Foam vs Fiberglass Insulation
Honest head-to-head — and which one is right for your project
(405) 659-1046There's no single winner in spray foam vs fiberglass. Each material does specific things better than the other, and the right answer depends on what you're insulating, where it is in the house, your budget, and how the rest of the building envelope is built. Premier Insulation installs both — and we recommend whichever fits the job, not whichever has the bigger margin. This guide covers the real-world differences, where each material wins, where each loses, and what we'd recommend in common Oklahoma scenarios.
Most comparisons online are written by manufacturers (biased toward their product) or generic SEO content (no local context). Premier has been installing both spray foam and blown fiberglass across the OKC metro since 2006 — this is the comparison we walk customers through during a free in-person estimate.
TL;DR — When to Pick Each
Standard attic floor reblow (existing home)
→ Blown fiberglassCost-effective, fills around obstacles, easy to top up later. R-38 of fiberglass on an attic floor performs comparably to spray foam at a fraction of the cost — assuming the ceiling plane is reasonably air-sealed (we check during the bid).
Attic conversion to conditioned space (foam the roof deck)
→ Spray foam (open cell)The single highest-impact use of spray foam in most Oklahoma homes. Brings the attic into the conditioned envelope — your HVAC equipment lives in a temperate space, ductwork stops leaking conditioned air into a 140°F attic.
New construction walls
→ Spray foam (open cell)Fills every cavity, seals air infiltration as it cures, dramatically quieter home. Cost premium pays back in 4-7 years from energy savings on a typical Oklahoma build.
Metal building or pole barn
→ Spray foam (open cell, sometimes closed cell)Fiberglass doesn't work well on metal — no cavity to fill, condensation risk on the cold metal surface. Spray foam bonds directly to the metal, insulates, and acts as a vapor barrier in one application.
Bonus room / room over garage that's always uncomfortable
→ Spray foam (open cell)These spaces are uncomfortable because of air leaks, not insufficient R-value. Foam fixes the underlying problem fiberglass batts can't address.
Limited budget, attic only, dry existing insulation
→ Blown fiberglass top-upMost cost-effective real-world way to lower an Oklahoma energy bill. Often qualifies for OG&E HEEP or Edmond Electric rebates that take a few hundred dollars off the bill.
Head-to-Head Comparison
| Category | Blown Fiberglass | Spray Foam |
|---|---|---|
| Cost (per square foot) | Lowest cost. Blown fiberglass is the cost-effective benchmark. | Open cell ~2-3× more than fiberglass. Closed cell ~4-5× more. Pays back through energy savings + air-seal benefits — but the upfront difference is real. |
| R-Value Per Inch | Blown fiberglass: ~R-2.9 per inch (R-38 = ~13 inches) | Open cell: ~R-3.6 per inch (R-38 = ~10.5 inches). Closed cell: ~R-7 per inch (R-38 = ~5.5 inches). Higher per-inch makes spray foam workable in shallow cavities where fiberglass won't fit. |
| Air Sealing | None. Air passes freely through the material — fiberglass insulates against conductive heat but doesn't stop air infiltration. | Excellent. Foam expands on contact and seals every gap as it cures. This is why R-30 of foam often outperforms R-30 of fiberglass by ~2× in real-world conditions — air infiltration is 25-40% of typical home heat loss. |
| Moisture | Loses R-value when wet, has to be removed and replaced. Vulnerable to roof leaks + plumbing leaks. | Closed cell is a vapor barrier — water won't pass through it. Open cell is vapor-permeable but doesn't lose R-value when wet (dries out instead). Better moisture tolerance overall. |
| Settling / Sagging | Settles ~10-20% over years (built into R-value calcs — settled depth is what matters). Doesn't sag in place once installed correctly. | None. Cures into a rigid (closed cell) or semi-rigid (open cell) mass that holds its shape and R-value for the life of the building — typically 80+ years. |
| Pest Behavior | Mice and squirrels nest in it readily — the fluffy material is comfortable nesting habitat. Pest-damaged fiberglass usually has to be removed-and-replaced. | Less attractive for nesting (no fluffy material to nest in), but mice and squirrels CAN and DO chew through both open and closed cell foam when motivated to reach the other side. Foam is not a pest barrier — neither material substitutes for sealing actual entry points (soffit gaps, plumbing penetrations, gable vents, etc.). |
| Sound Dampening | Some sound absorption — better than nothing, modest effect. | Open cell is excellent for sound — many customers choose it specifically for the noticeably quieter home (less road noise, less between-room transmission). One of the most-mentioned benefits in our customer feedback. |
| Installation Time | Fast — typical attic reblow done in a half-day to full day depending on size. Minimal disruption. | Slightly longer — typical residential job is one full day. Requires the homeowner to be out of the work area during application + cure (~2-4 hours). |
| Lifespan | 30-50 years in good conditions; less if it gets wet, pest-damaged, or compressed. | 80+ years. Designed for the life of the building. Doesn't degrade unless physically damaged. |
| Compatibility With Existing Insulation | Blow new fiberglass on top of existing fiberglass with no issue (most common Premier job). | Apply over fiberglass only with caveats. If switching from fiberglass to spray foam, we usually remove the old material first — better adhesion, cleaner end result. |
| Rebate Eligibility | Eligible for OG&E HEEP and Edmond Electric ceiling rebates (both rebate insulation upgrades regardless of material). | Same — both materials qualify for the standard utility rebates. Not the deciding factor. |
Common Misconceptions
Claim: “Spray foam is always worth the extra cost.”
Reality: False. For an attic floor with reasonable existing air sealing at the ceiling plane, blown fiberglass at the same R-value performs comparably for significantly less money. Spray foam earns its premium where air sealing matters most — walls, metal buildings, cathedral ceilings, conditioned attics, bonus rooms. On a typical attic floor reblow, fiberglass is usually the right answer.
Claim: “Same R-value = same performance.”
Reality: False. R-value only measures conductive heat loss, not air infiltration (25-40% of typical home heat loss). Spray foam's air-seal capability means R-30 of foam often delivers ~2× the real-world performance of R-30 of fiberglass. See our R-value page for the full mechanism.
Claim: “Closed cell is always better than open cell.”
Reality: False. Closed cell costs roughly twice as much per square foot and is needed only for specific applications (stem walls, underslab ductwork, exposed metal-building shop walls, commercial freezer/refrigerator spaces). For typical residential walls and attics, open cell performs comparably for half the price.
Claim: “I have a metal building so I have to use closed cell.”
Reality: Almost never. Closed cell has four real advantages over open cell — condensation control, vapor barrier, structural rigidity, and contact durability. On a typical metal building, open cell matches the first three at under half the cost (it handles condensation on metal just as well, has comparable vapor performance for the application, and far outperforms closed cell on sound dampening — a real benefit in an echo-prone shop). The only category where closed cell genuinely wins is contact durability: the foam stays exposed as the finished interior surface and won't dent if you bump into it. The fix is simple — most of our metal-building customers sheath the lower 8 feet of interior walls with OSB, which protects the open cell foam from contact damage AND gives a workshop-friendly surface for hanging shelves, workbenches, and tool hooks. The savings from open cell vs closed cell more than pays for the OSB. The real proof isn't the spreadsheet — we have repeat commercial customers who used closed cell exclusively for years across multiple buildings, then we did one open cell job for them and they haven't gone back since. Contractors and shop owners who've actually used both, side by side, on the same kind of building, are the ones who keep choosing the one that performs better and is more affordable at the same time.
Claim: “Spray foam off-gases for years.”
Reality: False with modern, properly-installed product. Properly installed open and closed cell foams are odorless within 24 hours and meet current safety standards. The horror stories online are mostly about jobs done with off-spec product or improper mix ratios — both avoidable with a qualified contractor.
Claim: “You can't add fiberglass on top of existing fiberglass.”
Reality: False. Blowing new fiberglass on top of existing material is one of the most common Premier jobs — the new layer settles cleanly over the old. The exception is if the existing material is wet, fire/smoke damaged, pest-contaminated, or badly compressed; in those cases removal is required first.
Common Questions
Bottom line — which one should I get?
It depends on what you're insulating. Standard attic floor with dry existing material = blown fiberglass top-up to R-38 (most cost-effective). New construction walls or attic conversion = open-cell spray foam (the air-seal benefit pays back fast). Metal building, bonus room, cathedral ceiling, anything where air sealing matters as much as R-value = spray foam. Premier walks you through the right answer for your specific project during the free estimate — we install both products and recommend whichever fits the job.
How much more does spray foam cost than fiberglass?
Open cell spray foam typically runs 2-3× the per-square-foot cost of blown fiberglass. Closed cell runs 4-5× the cost. The premium pays back through energy savings (4-7 years typical) plus the air-sealing and durability benefits — but the upfront difference is real. We give you both numbers in writing so you can decide based on your budget and project.
If spray foam is so much better, why do you still install fiberglass?
Because it's the right answer for many jobs. A dry, well-air-sealed attic floor reblow doesn't need spray foam's air-sealing premium — the air seal isn't doing anything if it's already sealed. Fiberglass at R-38 in that scenario performs equivalently to spray foam at R-38 for a fraction of the cost. Recommending spray foam where it isn't earning its premium would be selling you something you don't need. We'd rather get the answer right than maximize ticket size.
Can I do part of the house in foam and part in fiberglass?
Absolutely — and we often do. Common combo: open-cell spray foam in walls + cathedral ceilings + bonus room (where air sealing matters), blown fiberglass on standard attic floors (where it's the cost-effective answer). Mixing materials lets you put your money where it earns the most return.
Does spray foam help with allergies and indoor air quality?
Yes — by sealing air infiltration paths, spray foam dramatically reduces the amount of outdoor air (and the dust, pollen, and pollutants in it) leaking into your home. Combined with proper HVAC filtration, customers with seasonal allergies often notice a meaningful improvement after spray foam work. Fiberglass doesn't air-seal, so no equivalent benefit there.
Do you offer free estimates?
Yes — every estimate is free, written, and includes a clear recommendation of which product is right for your specific project + why. Call (405) 659-1046 or fill out our contact form to schedule one.
“Professional, quick, easy insulation job and no mess too! Made such a difference in the summer heat and helped lower my electric bills. Thanks Premier Insulation!”
— Kim Caplinger