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Comparing Blown Spray foam Insulation vs Fiberglass Costs, Types and R-Values

Is spray foam or fiberglass insulation better? It really depends on your budget and the purpose. Let’s compare spray foam insulation and fiberglass insulation, two of the most commonly used home insulation types.

Spray Foam Insulation vs Fiberglass Insulation

Spray foam insulation:

  • Has a higher R-value per inch of insulation thickness, especially closed cell foam insulation
  • Offers waterproofing/moisture barrier benefits that fiberglass cannot
  • Costs more to get the same insulation value (R-value)

That’s the bottom line. Let’s compare spray foam insulation vs fiberglass insulation cost, types available and R-value (Resistance to heat transfer).

Cost of Spray Foam vs Fiberglass Insulation

Comparing the cost of spray foam insulation to fiberglass insulation is tricky because they are priced differently.

So what we did is to crunch some numbers to determine spray foam insulation cost vs fiberglass to achieve recommended insulation values in different parts of your home.

Here are fiberglass insulation vs spray foam cost comparisons:

Costs are per square foot of installation. The first line is DIY – the cost of the installation and materials to install it. The second line is the cost to have the installation professionally installed.

2×4 Walls 2×6 Walls Crawlspace/Floor Attic Attic
R-13 R-21 R-30 R-40 R-60
Fiberglass DIY $0.35 – $0.40 $0.70 – $0.80 N/A $1.35 – $1.70 $2.00 – $2.50
Fiberglass Installed $1.30 – $1.65 $1.75 – $2.10 N/A $2.40 – $3.20 $4.25 – $5.30
Open Cell SPF DIY $2.20 – $2.50 $3.50 – $3.85 $5.15 – $5.75 $6.75 – $7.30 $10.00 – $11.50
Open Cell Installed $3.70 – $4.35 $5.90 – $6.95 $9.10 – $10.25 $10.90 – $11.55 $14.85 – $16.65
Closed Cell SPF DIY $2.50 – $4.00 $3.80 – $5.95 $5.60 – $7.50 $7.25 – $12.50 $12.80 – $16.50
Closed Cell Installed $4.00 – $5.85 $6.20 – $8.95 $9.55 – $12.00 $11.40 – $16.75 $17.65 – $21.65
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Fiberglass installation labor cost is about $1.00 to $2.75 per square foot based on the amount of insulation and the location.

Spray foam insulation for both types starts at about $1.50 per square foot and can cost more than $5.00 per square foot when a thick application is applied.

SPF insulation cost is determined by the board foot, which is 12”x12”x1” – a square foot of insulation 1 inch thick. Spray foam insulation price starts at about $0.60, or 60 cents, per board foot for DIY open-cell SPF with a top cost of about 80 cents.

Closed cell spray foam insulation cost is $1.25 – $2.00 per board foot for the material/DIY.  

Fiberglass batt insulation is priced by the roll or by the square foot. For example, roll insulation suitable for 2×4 wall and ceiling cavities is about $0.35 to $0.40 per square foot.

Fiberglass Insulation Types

Fiberglass insulation is produced in rolls, the most popular type, but loose material for blown in fiberglass installation is available too. Fiberglass is primarily silica that is heated and spun into fibers. Think cotton candy, but made with sand (silica) instead of sugar.

The glass does a good job of reflecting heat – that’s R-value or heat reflecting value. And relative to other types of insulation including spray foam, wool and cellulose, fiberglass is inexpensive. You get good bang for your buck, and that is why fiberglass insulation remains one of the most popular types. It is also DIY-friendly.

Cut-to-length rolls offer the most versatility and are great for attics. Batts cut in various lengths from 8 feet to 12 feet make wall installation quick and easy. It’s also available in various thicknesses.

Your options are faced and unfaced fiberglass insulation.

Faced: This product includes a vapor barrier as the “face.” It is installed in exterior walls (basements too) and in attic ceilings. The vapor-barrier faced side should face you as you install it. The facing has a flange on the sides that can be used to staple it to wall and ceiling framing. The facing is not waterproof.

Unfaced: Fiberglass insulation that is unfaced is used to bulk up the insulation in attics and elsewhere. If you live in a cold climate, for example, and have heating bills higher than you’d like, increasing attic insulation with rolls of unfaced fiberglass insulation is a cost-effective plan. In fact, adding fiberglass or cellulose insulation to the attic is a project with a cost to value/ROI of 100% or more.

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Spray Foam Insulation Types

This insulation is also called SPF, or spray polyurethane foam. There are two types of SPF

Open cell spray foam is lighter and has a lower R-value because gases in the material escape as it cures. It’s cheaper too, though more expensive than fiberglass for the same R-value.

Closed cell spray foam is dense and has a high R-value relative to open cell and fiberglass insulation. It costs more but also does a better job of controlling energy loss – and energy cost.

Both seal the space and provide an air/moisture barrier, something fiberglass insulation cannot do.

Note: Installing any insulation in attic ceilings should only be done when the attic is fully sealed and the air is “treated,” meaning heated and air conditioned.

R-Value Comparison

How well does fiberglass insulation insulate vs spray foam insulation? R-values are measured by the inch – how much insulation value does each give you per inch of thickness?

  •  Fiberglass insulation R-value = 2.8 to 3.7
  • Open cell SPF insulation R-value = 3.5 to 3.8
  • Closed cell SPF insulation R-value = 6.0 to 7.0

Perhaps it is obvious, but the higher the R-value, the more resistance the material has to the transfer of heat – that is, keeping heat where you want it: inside in the winter and outside in summer. It works both ways.

This chart gives you R-values for various applications.

Type 3.5″ 5.25″ 10″ 15″
Fiberglass R-9.8 to R-13 R-14.7 to R-17.8 R-28 to R-34 R-42 to R-51
Open Cell SPF R-12.3 to R-13.3 R-18.4 to R-20 R-35 to R-38 R-52.5 to R-57
Closed Cell SPF R-21 to R-24.5 R-31.5 to R-36.8 R-60 to R-70 R-90 to R-105

SPF insulation is rarely used in thicknesses of 10 or 15 inches. We’ve included those values for the R-value comparison of spray foam insulation vs fiberglass insulation.

Quick Comparisons and Installation Tips

  1. The cost of spray foam insulation vs fiberglass is higher if you choose closed-cell foam. Open cell foam installation also costs more, but not much. Either type gives you the advantage of sealing the area if properly installed. Foam is preferred for any location that might be damp – like basement or crawlspace walls.
  2. DIY spray foam insulation cost vs fiberglass is a closer comparison. Kits are available that include the material and applicator. Total cost starts at less than $1 per board foot for open cell spray foam insulation.
  3. When comparing spray foam insulation vs fiberglass batts, consider that fiberglass might settle over time or sag if it isn’t properly fastened. But if the wall or ceiling surface isn’t properly prepared, the foam might pull away from the surface. Additionally, if the spray isn’t evenly applied, a lot of heat can be lost or gained through thin spots.
  4. When comparing spray foam insulation vs fiberglass insulation r value, you get more insulation value with foam. If space is tight, and you can only install a thin layer of insulation, closed cell foam is by far the better choice. Spray foam insulation vs fiberglass r value is about equal for open cell insulation and about double for closed cell insulation per one-inch layer.
  5. Considering DIY blown fiberglass insulation vs spray foam, both require care to get the thickness right. Home improvement stores will often rent you a machine to blow in the fiberglass. Buy enough insulation, and they sometimes give you free use of the machine for a day.
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