Fiberglass Insulation NRC Ratings for Sound Absorption
Home theater, podcast studio, band practice room, home gym, home office. Same physics, same material, different thickness. Match your project to the NRC value below and skip the specialty acoustic panels.
NRC Value by Fiberglass Batt Thickness
Independently tested per ASTM C423, mounting Type A. These NRC values apply to standard-density fiberglass insulation across the R-value range we ship.
NRC is a broadband average across the 250, 500, 1000, and 2000 Hz frequency bands. Low-frequency absorption (below 125 Hz) is typically lower than these NRC values indicate — if you need bass trapping, use thicker batts or a purpose-built bass trap.
Which R-Value for Which Room
Residential and DIY acoustic projects, matched to the fiberglass thickness that gives you the right NRC without over-engineering.
Fill 2x6 wall cavities and ceiling joists with 6-inch unfaced fiberglass. Absorbs 85% of mid- and high-frequency reflections. Pair with acoustic drywall on the visible surface for full room treatment. Order unfaced R-19 ›
Standard 2x4 wall cavity fill. Absorbs enough reflection to eliminate the “room sound” that ruins voice recordings. Add absorber panels on the wall in front of the microphone position for extra treatment. Order R-13 ›
Fill 2x6 walls and ceiling with 6-inch unfaced. Resilient channel or Green Glue between the studs and drywall reduces sound transmission to adjacent rooms. Focus on transmission loss (STC), not just absorption (NRC). Order unfaced R-19 ›
Dumbbell drops and treadmill impact travel through the ceiling more than the walls. Prioritize ceiling insulation. Adding a rubber floor mat with mass loaded vinyl underneath addresses the impact side. Order R-19 ceiling ›
Reduces the hollow, hard-surface echo that makes video calls sound unprofessional. R-13 in the walls plus a rug and one soft-surface wall covering (curtains, canvas art) is usually enough for meetings without dedicated acoustic panels. Order R-13 ›
HVAC noise is broadband and continuous. Insulating the room walls plus wrapping the ductwork itself with acoustic duct liner cuts perceived noise dramatically in adjacent living spaces. Order unfaced R-19 ›
NRC vs STC — Absorption vs Transmission
NRC (Noise Reduction Coefficient) measures how much sound the material absorbs inside the room. Higher NRC means a quieter, less reverberant room. Fiberglass insulation gives you 0.55–0.90 NRC depending on thickness.
STC (Sound Transmission Class) measures how much sound is blocked from passing through the wall to the next room. Higher STC means less noise bleeding into adjacent spaces. Standard fiberglass insulation in a 2x4 wall gives you STC 39; upgrade to 2x6 with staggered studs and resilient channel to hit STC 55+.
Acoustic Insulation FAQ
Can I use faced insulation for soundproofing?
Yes, but unfaced performs slightly better for acoustic absorption. If code requires a vapor retarder in your wall assembly, foil-faced or vinyl-faced fiberglass will still absorb 0.50–0.80 NRC depending on thickness — only 0.05–0.10 lower than unfaced. For pure acoustic treatment where vapor retarders are not required, choose unfaced.
How does fiberglass compare to mineral wool for soundproofing?
At equal thickness, fiberglass and mineral wool (rock wool) have nearly identical NRC values. Mineral wool has slightly higher density (about 2.5 pcf vs 0.75 pcf for fiberglass), which gives it marginally better low-frequency absorption below 250 Hz. For most residential acoustic projects, the difference is not audibly significant and fiberglass costs 30–50 percent less per square foot.
Does spray foam insulation absorb sound as well as fiberglass?
No. Closed-cell spray foam has an NRC of about 0.15 — it reflects most of the sound striking it instead of absorbing it. Open-cell spray foam is better (NRC around 0.60) but still trails fiberglass. If sound absorption matters, fiberglass batts are the right material regardless of whether spray foam is your thermal envelope.
Do I need to seal the wall cavity for good acoustic performance?
Yes for STC (transmission loss). Any gap around outlets, switches, ductwork, or trim carries sound directly through the wall assembly and defeats the insulation’s absorption. Caulk every penetration with acoustic sealant. This step is often the difference between a wall that sounds “better” and one that measurably blocks noise.
How much fiberglass do I need for a 10x12 home theater?
A 10x12 room has approximately 176 square feet of wall area (10 + 12 + 10 + 12 = 44 ft perimeter x 8 ft ceiling) plus 120 square feet of ceiling. Order 300 square feet of R-19 unfaced batts (2x6 wall depth) or 250 square feet of R-13 (2x4 wall depth) to fill the assembly with 10 percent waste factor. Use our calculator to see wholesale pricing.
Building a Sound-Sensitive Room?
Text me your room dimensions and what you are treating (home theater, podcast, gym, etc.). I will spec the exact R-value and quantity for your project — usually in under 30 minutes.