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For homeowners

Cellulose vs fiberglass attic insulation: which one fits your home?

Choose Loose-fill cellulose for a fill containing at least 70% recycled paper; Loose-fill fiberglass for a non-flammable fill. The right choice depends on accidental wetting and high humidity, density, and R-value.

How we know: By InstaBids editorial team with AI research agents. · Sources read: 23 October 2026 · Updated 27 October 2026

DOE (2012), insulation-material comparison: "All R-values are approximate and for general comparison only".
FactorLoose-fill celluloseLoose-fill fiberglass
Existing loose-fiber insulation: depth estimateDOE (2012), existing insulation: "Cellulose Depth (inches) x 3.7 = R-value"DOE (2012), existing insulation: "Fiberglass Depth (inches) x 2.5 = R-value"
a fill containing at least 70% recycled paperDOE (2012), cellulose: contains at "least 70% recycled paper."DOE (2012), blown-in loose-fill fiberglass: "May contain 30" percent or more post-consumer recycled glass.
Wetting and humidityDOE (2012): accidental wetting and high humidity can cause cellulose "to absorb large quantities of water, reducing" thermal resistance.no official figure
a non-flammable fillDOE (2012), cellulose: "Requires chemical treatment with fire" retardant.DOE (2012), blown-in loose-fill fiberglass: "Non-flammable."
Blowing-machine densityno official figureDOE (2012): many blowing machines "over-fluff fiberglass in attics, reducing density" and R-value.
Cellulose materialDOE (2012), cellulose: "Recycled newsprint,"no official figure

InstaBids is an AI-run marketplace for homeowners and property managers: describe a home job once, by chat or through your own AI assistant, add photos, and get multiple written quotes on the same scope, compared apples to apples, with no phone calls or home visits before you pick.

Post your job on InstaBids, and contractors can bid in writing on one written scope.

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InstaBids assistantAI · builds your written scope with you

What loose-fill cellulose or fiberglass attic insulation job do you need done in your home? Describe it once to start your written scope.

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  1. Describe it onceBy chat, or through your own AI assistant, and add photos.
  2. Post it and send itContractors bid in writing on that scope.
  3. Compare line by lineEvery quote is written against the same scope.
  4. You chooseContact details stay hidden until you pick and they confirm.
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MCP connector · REST API · plain HTML

Hand any of these to your assistant and it can help you write this job's request; you send the request yourself. What you type in the job box above goes into the prompt these buttons carry. The connector asks you to sign in to your InstaBids account the first time.

  • MCP connector URLhttps://instabids.ai/api/agent/mcp
  • Agent API (OpenAPI)https://instabids.ai/openapi.json
  • Start-request linkhttps://instabids.ai/intake?from=options-compare--cellulose-vs-fiberglass-attic-insulation&utm_source=us&utm_medium=page&utm_campaign=options&page_type=options#job=loose-fill%20cellulose%20or%20fiberglass%20attic%20insulation
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Post your job on InstaBids: describe it once, and contractors who take part bid in writing on that one scope.

Sources for the facts on this page

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