Cellulose

Summary

Cellulose insulation is loose-fill made mostly from recycled paper, hammer-milled and treated with boric acid or ammonium sulfate, about 75 to 85 percent paper fiber. It has the highest recycled content of any insulation and about R-3.8 per inch, but settles 13 to 20 percent unless dense-packed.

Cols

Image

Dry (loose-fill): blown into attics or existing walls
Dense-pack: loose-fill installed at higher density to reduce settling
Wet-spray: water added during spraying; wall dries at least 24 hours before covering
Stabilized: lightly wetted to activate an adhesive; used mainly in attics and sloped roofs (approved up to 5:12)
Low-dust: contains a small amount of oil
Borates: boric acid fire retardant, a mined resource

History and demand

Invention

1950s: modern versions begin

First uses in construction

1772: Monticello insulated with a form of cellulose
1970s: wide United States use after the 1973 to 1974 oil embargo; 1978 federal safety standards followed; by 1991 only 61 United States producers remained
1985: CPSC requested repeal of the flammability standard (16 CFR Part 1209)

Sourcing

United States: GreenFiber is the largest named producer, with eight plants and about 350,000 tons of recovered fiber used a year; fiberglass still holds about 94 percent of the US insulation market
Feedstock is mostly recycled old newspaper, with recycled cardboard replacing it as newsprint supply shrinks

Composition and production

Raw materials

75 to 85 percent recycled paper fiber (waste newspaper) and the rest fire retardant (boric acid or ammonium sulfate), which also makes it less attractive to pests

Properties

Thermal and moisture

Thermal conductivity: about 40 mW/(m·K), roughly R-3.8 per inch; comparable to glass or rock wool, lower than closed-cell polyurethane foam (about R-5.5 to 6.5 per inch)
Settling: dry loose-fill can settle 13 to 20 percent

Uses in buildings

Building elements

Wall and Roof Insulation: loose-fill attic insulation, and dense-pack or wet-spray insulation in wall and roof cavities
Wood-Framed Walls: cavity insulation between studs

Pros and cons

Pros

Highest recycled content of any insulation
Less expensive per unit of R-value than foam
Density gives a slight sound-reduction advantage over fiberglass

Cons

Dust during installation; possible ammonia odor with ammonium sulfate
Roughly three times as heavy per square foot as fiberglass for the same R-value
Some evidence of mold in buildings with wet-spray dense-pack insulation, especially with a vapor barrier

Sustainability

Embodied carbon

Reported to have the lowest embodied energy of common insulation types (a claim of 20 to 40 times less than furnace-made products lacks a citation)

Health

No VOC emissions; earned M1 and NaturePlus indoor air quality certifications

Manufacturing and cost

Main manufacturers and suppliers

Greenfiber

Sources

Wikipedia: Cellulose insulation, https://en.wikipedia.org/wiki/Cellulose_insulation
Wikimedia Commons: Bulk recycled cellulose.jpg, photo by Okram (CC BY-SA 3.0), https://commons.wikimedia.org/wiki/File:Bulk_recycled_cellulose.jpg
Recycling International: recycled paper gains foothold in insulation market, https://recyclinginternational.com/commodities/paper-and-cardboard-recycling/recycled-paper-gains-foothold-in-insulation-market/6554/
GreenBuildingAdvisor: shrinking supplies of old newspapers challenge cellulose manufacturers, https://greenbuildingadvisor.com/article/shrinking-supplies-of-old-newspapers-challenge-cellulose-manufacturers