Blown-In Insulation R Values: Loose-Fill Chart (Cellulose, Fiberglass, Wool)

“How much R-value does blown-in insulation have per inch?”

With blown-in insulation (also referred to as loose-fill insulation), the R-value per inch is the key data point. Blown-in insulation can have R-values from R-1 per inch and up to R-3.4 per inch (loose-fill cellulose). We are going to list all blown-in insulation R-values per inch (check the chart below).

Namely, we use blowing machines to add loose-fill insulation. To adequately plan the overall R-value, we need to know what is the R insulation value per inch for these blown-in insulation materials.

Example: In California, you need R-49 to R-60 attic insulation (you can check the recommended attic R-values chart here). How thick should you blow the loose-fill insulation? The prerequisite for calculating this accurately is by knowing what is the R-value per inch of your insulation material.

blown in fiberglass 8 inch insulation on attic floor
Adding 6-8 inches of blown-in fiberglass insulation to the attic floor (R-18.6 to R-24.8).

Not all blown-in insulation materials have the same R-value. This loose-fill insulation is made out of small particles of cellulose, rock or mineral wool, fiberglass, perlite, vermiculite, and even wood chips.

Each type of blown-in insulation has its own insulation R-values per inch, with blown-in cellulose having the highest R-3.4 per inch insulation capacity.

Here is the chart that lists all major blown-in insulation R-values per inch, per 2-inches, per 4-inches, and per 8-inches (with commentary):

Blown-In Insulation R-Value Chart (Per 1, 2, 4, 8 Inches Thickness)

Blown-In Insulation Material: R-Value Per Inch: 2 Inch R-Value: 4 Inch R-Value: 8 Inch R-Value:
Blown-In Cellulose R-3.4 Per Inch R-6.8 R-13.6 R-27.2
Blown-In Wool R-3.1 Per Inch R-6.2 R-12.4 R-24.8
Blown-In Fibergrass R-3.1 Per Inch R-6.2 R-12.4 R-24.8
Blown-In Perlite R-2.7 Per Inch R-5.4 R-10.8 R-21.6
Blown-In Vermiculite R-2.25 Per Inch R-4.5 R-9 R-18
Blown-In Wood (Wood Chips) R-1 Per Inch R-2 R-4 R-8

As you can see, the blown-in insulation materials are listed from the highest R-value (cellulose) to the lowest R-value (wood chips). The best per-inch loose-fill insulation material is cellulose, followed closely by mineral wool and fiberglass:

  • Blown-in cellulose has an R-3.4 per inch insulation value. If you blow an 8-inch layer, you are adding R-27.2 of insulation.
  • Blown-in mineral wool has an R-3.1 per inch insulation value. If you blow an 8-inch layer, you are adding R-24.8 of insulation.
  • Blown-in fiberglass has an R-3.1 per inch insulation value. If you blow an 8-inch layer, you are adding R-24.8 of insulation.
  • Blown-in perlite has an R-2.7 per inch insulation value. If you blow an 8-inch layer, you are adding R-21.6 of insulation.
  • Blown-in vermiculite has an R-2.25 per inch insulation value. If you blow an 8-inch layer, you are adding R-18 of insulation.
  • Blown-in wood chips have an R-1 per inch insulation value. If you blow an 8-inch layer, you are adding R-8 of insulation.

This explains why we use loose-fill cellulose, mineral wool, and fiberglass for heavy insulation rooms (like the attic). In most cases, you will see blown-in cellulose use over mineral wool because it is cheaper (usually made from recycled newsprints).

Loose-fill perlite and vermiculite were used in the past; you will almost never see them in new constructions. The same goes for wood chips. The listed R-values per inch here can help you calculate the R-value of existing buildings.

Hopefully, this chart illustrates well the R-values of blown-in insulation materials and will help you adequately calculate what thickness of blown-in insulation you need. If you have any questions or suggestions, you can freely use the comment section below.

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