Will cellulose settle and reduce R-value?

Generally, loose-fill cellulose can settle over time if installed at low density, which reduces depth and effective R-value. Dense-pack methods or installing to manufacturer-specified installed density reduce settling. Periodic inspection of attic depth and topping up loose-fill cellulose can restore design R-values.

Is fiberglass safer or healthier than cellulose?

Both materials have handling considerations. Fiberglass can irritate skin and lungs during install; wear gloves, long sleeves, and a NIOSH-rated respirator. Cellulose is dusty during blowing and also needs respiratory protection (P100 recommended). Cellulose is treated with borate for pest and mold resistance; borates have a long safety record in building materials when used per instructions.

Can I mix cellulose and fiberglass in the same assembly?

Yes—hybrid assemblies are common. For example, exterior continuous insulation with an interior cavity filled with cellulose or fiberglass combines the benefits of both materials. Avoid layering different loose fills directly on top of one another in a way that could trap moisture; keep clear drying paths and coordinate vapor control.

Which one is better for soundproofing?

Cellulose generally outperforms fiberglass at reducing low-frequency sound because of its density and ability to fill voids. Mineral wool (rockwool) is another strong sound-control option; compare it to fiberglass in our rockwool vs fiberglass comparison if acoustic performance is a priority.

Do either of these prevent air leaks?

Neither cellulose nor fiberglass is an air barrier by itself. Air sealing—sealing gaps, rim joists, and penetrations—must be done before insulation is added. Cellulose and dense-pack installations reduce airflow through cavities better than loose fiberglass, but a continuous air barrier (taped sheathing or interior membrane) is still required for best airtightness. See our air-sealing tools and materials guide for practical steps.

Cellulose vs Fiberglass Insulation: Complete Comparison

Insulation & Building Envelope

Practical, side-by-side comparison of cellulose and fiberglass insulation — performance, installation, durability, sustainability, and when to choose each.

By Graham Mann | Published: 6/23/2026

Cellulose vs Fiberglass Insulation: Complete Comparison Choosing between cellulose vs fiberglass insulation matters for every budget-conscious DIY builder. This article explains how the two materials differ in thermal performance (R-value), installation method (blown-in vs batts), air-sealing behavior, moisture response, fire and pest resistance, embodied carbon, and DIY difficulty—so you can pick the right product for an attic retrofit, wall cavities on a self-build, a tiny house, or an off-grid cabin. For external source context, review Cellulose Vs Fiberglass Insulation: Complete 2025 Guide - SolarTech. TL;DR: - Cellulose typically delivers about 3.2–3.8 R/in and fills irregular cavities well; good for attic retrofits and dense-pack wall fills. - Fiberglass batts are lower density (around 2.2–2.9 R/in) but stable and easy to buy; best for new stick-frame walls and DIY batt installs. - For very cold climates or long-term performance, prioritize air sealing and continuous exterior ins...

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