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A worker in a dust mask blowing loose-fill insulation across an attic floor through a wide hose

Cellulose and blown fiberglass

Blown-in insulation cost

Blown-in is the cheapest way to hit a high R-value in an attic. Materials run $0.30–$0.54 per square foot at R-30; professional installation is $1.05–$2.10.

DIY material
$0.30 – $0.54per sq ft at R-30
Installed
$1.05 – $2.10per sq ft at R-30
Per bag, cellulose
$10 – $16about 1,200 R·sq ft each
Blower rental
$0 – $100often free with a bag minimum

Quick numbers

DIY material

$0.30–$0.54

per sq ft at R-30

Installed

$1.05–$2.10

per sq ft at R-30

Typical attic

$900–$2,400

1,200 sq ft to R-49, installed

Cost per bag, and how many you need

Bags are priced roughly $10–$16 for cellulose and$32–$48 for blown fiberglass, but fiberglass bags cover considerably more area, so per unit of R-value they land close together.

Coverage is linear in R-value, which means one constant describes the whole chart. For cellulose that's about 1,200 R·square-feet per bag:

Bags = (area × R-value added) ÷ 1,200

A 1,200 sq ft attic adding R-40 needs (1,200 × 40) ÷ 1,200 = 40 bags, plus 10% waste = 44 bags. At $12 a bag that's about $528 in material.

Cellulose or blown fiberglass?

Close-up of loose cellulose insulation — gray shredded recycled paperCellulose

Blown cellulose

R per inch
3.5
Depth for R-49
14 inches
Material at R-30
$0.30–$0.48
Settles
10–20%
  • Fills gaps and voids batts leave open
  • Roughly 80% recycled content
  • Better at damping airborne sound
  • Denser, so it resists air movement

Choose this when: Most attic retrofits, especially with obstructions or awkward corners.

More on cellulose
Pink blown fiberglass filling the joist bays of an attic floor, with a printed R-value depth gauge standing in itBlown fiberglass

Blown fiberglass

R per inch
2.5
Depth for R-49
19.6 inches
Material at R-30
$0.33–$0.54
Settles
Minimal
  • Lighter — matters on older ceiling framing
  • Sheds water rather than absorbing it
  • Does not settle appreciably over time
  • Non-combustible

Choose this when: Weight-sensitive framing, or where occasional dampness is likely.

More on blown fiberglass

For most attic retrofits cellulose gives better real-world performance for similar money. Choose blown fiberglass when ceiling framing is old and weight matters, or where occasional dampness is likely.

Blower rental

Budget $0–$100. Most major retailers waive the rental fee entirely with a minimum bag purchase — often around 10–20 bags, which most attic jobs exceed anyway. Ask before paying; it is not always offered unprompted.

Machines are trailer-towable or fit in a pickup. You'll want two people: one loading the hopper, one on the hose in the attic.

Dense-packing existing walls

Blowing insulation into closed wall cavities costs $1.50–$3.50 per square footinstalled. Crews drill holes in each cavity, blow to high density, then plug and patch.

This is not a DIY job. Achieving correct density matters — under-packed cavities settle and leave a gap at the top, which is worse than nothing — and it needs a machine that reaches dense-pack pressures. Exterior siding removal may also be involved.

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