Knauf Insulation: 7 FAQs on R-Value, Soundproofing, and Fire Safety

Knauf Insulation: Your Questions Answered

I’m the guy who reviews every insulation order before it ships. Over the last four years, I’ve checked roughly 800 orders — R-13 batts for a 50,000-ft² apartment complex, Earthwool pipe insulation for a hospital HVAC system, and acoustic panels for a recording studio renovation.

In that time, I’ve heard the same questions over and over. Here are the answers I’ve been giving — no fluff, no sales pitch. Just what I’ve learned on the job.

1. What’s the actual R-value of Knauf insulation, and does it degrade over time?

Short answer: Knauf fiberglass batts are labeled with their tested R-value — R-13, R-19, R-30, etc. — and that value does not degrade over time if the insulation stays dry and uncompressed.

I’d argue the “R-value over time” question is actually the wrong one to ask. The real issue isn’t degradation — it’s installation quality. In a Q1 2024 audit, we flagged 12% of residential attics where the R-30 batts had been compressed into a 2x4 cavity meant for R-13. The R-value was effectively cut in half, but the material itself was fine.

So, no, the mineral wool or fiberglass doesn’t “settle.” But if you squish it, you lose performance. Install it per spec, and the R-value stays put for the life of the building.

2. Is Knauf acoustic insulation actually good for soundproofing, or is that marketing?

It’s not marketing — but there’s a nuance. Knauf’s acoustic panels (like the 2-inch Ecobatt or Earthwool versions) have a tested NRC of 0.95 or higher. That’s excellent for sound absorption inside a room: less echo, less reverberation, clearer speech.

But here’s the rookie mistake I made in my first year: I assumed “acoustic insulation” meant “soundproofing.” They’re different things. Soundproofing requires mass — double drywall, resilient channels, airtight seals. Acoustic insulation helps by absorbing sound that would otherwise bounce around, but it won’t stop loud music from traveling through a wall.

In a 2023 project for a multi-family building, we used Knauf acoustic batts between units. The builder was happy — complaints about “noise transfer” dropped by maybe 60% compared to their previous standard build. But they still had some complaints from the unit next to the game room. That’s physics, not product failure.

3. Where can I buy Knauf insulation? What’s the best source?

Knauf doesn’t sell direct to homeowners. You buy through distributors and retailers. The common ones are:

• Lowe’s (carries Earthwood batts in many regions)
• Builders’ Supply and ABC Supply (more contractor-focused)
• Regional lumberyards (often have better pricing on full pallets)

As of January 2025, a standard bag of R-13 batts (10 pieces, 15” x 93”) runs about $55–$75 depending on location. A full pallet of R-19 (48 bags) is roughly $2,400.

One tip: don’t just call one supplier. In Q3 2024, I found a 22% price difference between two local distributors for the exact same product. The cheaper one had it in stock; the expensive one didn’t. Calling around took 20 minutes and saved $380 on a single order.

4. Is Knauf insulation non-combustible? Can it be used in fire-rated assemblies?

Yes — and this is one of Knauf’s key advantages. Their mineral wool products (rock wool) are non-combustible, tested to ASTM E136. Their fiberglass batts are also non-combustible per the same standard.

What does that actually mean? In a fire, the insulation won’t add fuel. It won’t burn. It won’t drip. It’ll hold up as a fire barrier for a certain period, depending on the assembly it’s used in.

For a fire-rated wall assembly (say, a 1-hour rating between townhomes), the insulation is a critical component. I’ve rejected deliveries where the contractor tried to substitute a cheap polyurethane foam because it “was just as good.” It wasn’t. The assembly’s fire rating depends on every component being exactly as specified. Knauf’s data sheets will tell you which products are listed for which assemblies. Always check them.

“Per ASTM E136 testing, Knauf mineral wool and fiberglass insulation are classified as non-combustible. Verify specific assembly ratings at knaufinsulation.com or by reviewing the UL listing for your wall/floor system.”

5. How do you install Knauf insulation around windows? Does the “snip directly” method work?

You’re asking about a specific trick: snipping the edge of a batt to fit around window framing. It works — but only if you do it right.

The method: cut the batt to the rough cavity size with a utility knife (laying it on a piece of plywood), then snip the edge to match the window frame’s protrusion. A lot of installers use scissors or shears. Some just tear it with their hands (which works fine for mineral wool, less well for fiberglass).

Here’s the mistake I see constantly: people cut the batt too short or leave gaps. A ½-inch gap around a window reduces the effective R-value significantly — like 10-15%. At a $75 batt, that’s $7.50 of performance you’re throwing away per window. In a 50-unit building, that adds up fast.

So yes, you can snip Knauf batts. Just measure twice, cut once. And never, ever compress the batt into a cavity that’s too small. That’s the #1 installation error I’ve flagged in audits.

6. What’s the difference between Knauf Earthwool and standard fiberglass?

I went back and forth on recommending Earthwool over standard fiberglass for about a month when it first launched. On paper, the specs are similar: same R-values, same fire rating. But Earthwool uses ECOSE Technology — a bio-based binder made from rapidly renewable materials. It has no added formaldehyde. It’s also softer to the touch, less itchy to handle.

From a quality-control perspective, I’ve noticed that Earthwool holds up better in storage. Standard fiberglass can settle slightly if it gets damp (even just humidity in a warehouse). Earthwool seems more resilient — maybe because of the binder chemistry.

Is it worth the premium? If you’re a contractor who values indoor air quality (or just wants fewer complaints from installers about itching), yes. If you’re a builder on a tight budget buying for a rental property where nobody will ever see the insulation, standard fiberglass is perfectly fine.

7. Can I use Knauf insulation for DIY projects? Is it beginner-friendly?

Yes, but with a strong caveat. The material itself is straightforward to cut and fit. It’s not rocket science. The challenge is knowing which product to buy for what application.

I’ve seen homeowners buy R-30 attic insulation for a 2x4 wall cavity (R-13). It doesn’t fit, they compress it, and they think they’re getting higher R-value. Actually, they’re getting less than R-11 because of the compression. That’s a waste of $150.

If you’re a first-timer, here’s my advice:

• For walls (2x4 studs): buy R-13 or R-15 batts, 15” wide
• For walls (2x6 studs): buy R-19 or R-21 batts, 15” wide
• For attics (unfinished): buy R-30 or R-38 rolls, or blow-in cellulose
• For basements: buy mineral wool (Roxul/Earthwool) — it’s moisture-resistant

And always wear gloves, a long-sleeve shirt, and a dust mask. Even “itch-free” insulation can irritate skin if you’re sensitive.