Material · Wood · Assembly
Cellulose Insulation
Dense-pack cellulose · recycled-fiber insulation
Insulation made from at least 80% recycled paper fiber, treated with borates for fire and pest resistance, and installed loose-blown in attics or dense-packed into walls. Dense-packing is the trick: it slows air movement through the cavity, doing air-sealing work most insulations cannot.
Why it matters
Cellulose is the value pick of high-performance retrofits: the lowest-carbon common insulation, made from recycled newsprint, with dense-pack installs that measurably cut air leakage in old walls. The borate treatment that makes it fire-safe is benign as building chemistry goes, and the material buffers moisture like the wood fiber it is. Installation quality is everything — the same material loose and settled performs nothing like it dense-packed by a pro.
Benefits
- Dense-pack slows air leakage through cavities — insulation that also air-seals
- Lowest embodied carbon of mainstream insulations; mostly recycled content
- Borate treatment resists fire, mold, and pests without harsh chemistry
- Hygroscopic buffering forgives minor assembly moisture
- Retrofits into closed walls without demolition
Best applications
Rooms: Whole home
Performance
Watch-outs
- Installer-dependent to an extreme: proper density or it settles and underperforms
- Dusty install — containment and cleanup matter
- Cannot handle bulk water; saturation means replacement
- Loose-fill attic depth settles ~15–20% — spec settled depth, not blown depth
What to verify
Finish, binder, sourcing, and installation conditions to confirm before specifying.
- Dense-pack density verified (3.5+ lb/ft³ in walls)
- Borate-only treatment — avoid ammonium sulfate blends (corrosion and odor history)
- Settled R-value spec for attics, not initial depth
- Installer's dense-pack track record and equipment
Certifications to look for
The labels that separate the real material from the marketing version.
CIMA technical standards
Cellulose Insulation Manufacturers Association installation standards
UL GREENGUARD (select lines)
Emissions certification on major brands
Sources
Information verified July 2026.