Fiberglass vs Mineral Wool: Which Is Right for Your Project?

Published June 2026 · By Prestige Insulation

Fiberglass and mineral wool are the two dominant batt insulation formats in residential and light commercial construction. Both work. Both meet code. The question is which one is right for a specific assembly, budget, and building type.

Quick Comparison Table

Factor	Fiberglass Batts	Mineral Wool (Rockwool)
Cost	Lower — typically 20–40% less per bag	Higher upfront cost
R-Value per inch	~R-3.1 to R-3.7	~R-3.7 to R-4.2
Fire resistance	Melts at high temp; non-combustible but not fire-rated	Non-combustible up to ~2,150°F; used in fire-rated assemblies
Moisture resistance	Can retain moisture; requires vapor control	Hydrophobic — repels water, dries quickly
Sound control (STC)	Moderate	Superior — preferred for party walls and floor-ceiling assemblies
Installation	Lighter, easier to handle	Denser, more rigid; holds shape better in cavities
Eco profile	30–40% recycled glass content	70–75% recycled stone/slag content

When to Choose Fiberglass

Fiberglass batts are the right call for most standard residential projects where cost control matters and there are no special fire, sound, or moisture requirements. They cover the vast majority of wall, floor, and attic applications at a lower material cost.

• Standard exterior wall cavities (2×4 or 2×6 framing)
• Attic floors and knee walls
• Floor assemblies over unconditioned crawlspaces
• Budget-sensitive projects where code minimums are the target

When to Choose Mineral Wool

Mineral wool earns its higher price tag in specific applications where its fire resistance, moisture performance, or sound control are worth the premium.

• Party walls and shared assemblies — mineral wool's density delivers significantly better STC ratings
• Fire-rated assemblies — SAFB (Semi-Rigid) and AFB are used in tested fire-rated systems
• High-moisture environments — crawlspaces, basements, below-grade applications
• Multifamily construction — sound and fire performance between units
• High-performance and Passive House builds — superior R-value per inch in thinner assemblies

Product Lines We Carry

Fiberglass: R-11, R-13, R-15, R-19, R-21, R-30, R-38, R-49 — kraft-faced and unfaced, standard and high-density grades, all standard widths (15" and 23").

Mineral wool: AFB (Acoustic Fire Batt), SAFB (Semi-Rigid), R-15, R-23, R-30. Available in 2×4, 2×6, and wider applications.