Comparisons
Mineral Wool vs Fiberglass
Mineral wool costs roughly 25–50% more than fiberglass and beats it on nearly every performance measure except price. Whether that matters depends on the wall.
Updated October 2026 · about 6 min read
Performance differences
Mineral wool: R-4.0 to R-4.3 per inch, non-combustible to about 2,150°F, hydrophobic, dense enough to friction-fit without stapling, and noticeably better at damping sound.
Fiberglass: R-3.1 to R-3.8 per inch, non-combustible but with a combustible facing when kraft-faced, lighter and cheaper.
Installation feel
Mineral wool cuts cleanly with a bread knife and holds itself in the bay — a real time-saver on ceilings and interior partitions. Fiberglass is floppier and needs stapling or support rods.
Gear for this job
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Cost
Expect roughly $1.10–$1.90 per sq ft for mineral wool batts versus $0.55–$1.20 for fiberglass at similar R-value. Over a whole house that difference is real; over one media room it is trivial.
Best uses
Mineral wool for interior sound walls, garage and mechanical room fire separations, exterior continuous insulation and anywhere that may get damp. Fiberglass for large-area, budget-driven work like attic floors and standard exterior walls.
Run the numbers
Frequently asked questions
- Is mineral wool worth the extra money?
- For sound walls, fire separations and damp-prone areas, yes. For bulk attic coverage, fiberglass or cellulose delivers more R per dollar.
- Does mineral wool need a vapor barrier?
- It is unfaced, so vapor control comes from a separate membrane, smart retarder or the drywall paint system according to your climate zone.
- Is mineral wool itchy?
- Less than fiberglass, but still wear gloves, glasses and a respirator — it creates dust when cut.
Insulation gear worth owning
The tools and materials that show up on almost every insulation job.
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