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Common Gas Flow Resistivity numbers.
Old 21st June 2020
Here for the gear

Knauf (UK) Response - Density and NRC

I recently contacted the UK office for Knauf and received these responses.

Although they did not have GFR figures, I thought it worth posting the numbers here anyway as they detail different densities for various thicknesses of the same product.

Used along with the NRC values perhaps we can make an informed guess at some GFR's for use in the porous absorber calculations (?).

From Knauf Technical Advisor 17th June 2020 :

Knauf Earthwool Building Slab RS45 (All thicknesses) – Nominal Density 45Kg/m³

100mm Knauf Earthwool Acoustic Roll – Nominal Density 10Kg/m³
75mm Knauf Earthwool Acoustic Roll – Nominal Density 10Kg/m³
63mm Knauf Earthwool Acoustic Roll – Nominal Density 13Kg/m³
50mm Knauf Earthwool Acoustic Roll – Nominal Density 16Kg/m³
25mm Knauf Earthwool Acoustic Roll – Nominal Density 19.5Kg/m³

And attached are the NRC values for some of these products.

Knauf Earthwool Acoustic Roll - Absorption Co-efficients
Knauf Earthwool Building Slab - Absorption Co-efficients

They had available only the NRC values for the 50S and 25S Knauf Earthwool Acoustic Roll and the Knauf Earthwool Building Slab RS33, RS45, RS60, RS80, RS100, RS140., all at various thicknesses.

I am guessing here, but presumably the "S" which represents a "Sold Backing" on their NRC results must mean that the material was against a boundary, and doesn't refer to a film on the absorbent material itself (?) because I don't see any backing on the Acoustic Roll in any images available online.

Last edited by Jimmy_2Tone; 21st June 2020 at 11:02 AM.. Reason: mistake..
Old 8th August 2020
Here for the gear
I live in Las Vegas NV, USA and am starting a new build. I am currently attempting email convo with OC, RW and JM as those are my options at Lowes and Home Depot. I got a response from Rockwool today that said specifically this:

The only product we have tested for air flow resistivity is our AFB® product.

- AFB® at 3” has an air flow resistivity of 16,600 mks rayls/m

- Safe’n’Sound® product is expected to have a slightly lower air flow resistivity than AFB® [~ 12,000 – 16,000 mks rayls/m]

- RockBoard® 40 & FabRock™ LT would have similar air flow resistivity to the AFB® product [~15,000 – 20,000 mks rayls/m]
- RockBoard® 60 will have an expected air flow resistivity of ~32,000 – 46,000 mks rayls/m
- RockBoard® 80 is expected to have an air flow resistivity of ~53,000 – 57,000 mks rayls/m – also Comfortboard™80

These numbers are estimates based off the density of the products and testing done by NRC back in 1995. The products have also been listed from least rigid to most rigid.

The Rockboard brochure in the link has ASTM C423 results but no AFR. interestingly, there is a really pretty control room picture at the top of the pamphlet.


OT and not to get anyone's hopes up, I've been having a really fun discussion with a rep at JM and I want to share with someone who will appreciate the humor I've found in a certain exchange.

When attempting to explain to the rep how we are using the material and the importance of AFR/GFR data, which she found extraordinary, she suddenly remembered what room the machine that tests AFR is in and how easy it would be to cut a plug and do the test. By the tone in her voice and her level of excitement I got the impression that she is an engineer too far removed from a solid day in the lab and that she would go down there and test the stuff herself if she thought she could get away with it.

That being said, she is currently talking an acoustical engineer who understands our plight and is looking into doing some testing. Of course any info has to pass company IP policy....
Old 15th September 2020
Here for the gear

Received these numbers from Owens Corning regarding their EcoTouch low density (fluffy) insulation:

R-11 = 2450 mks rayls/m

R-13 = 3500 mks rayls/m

R-15 = 5000 mks rayls/m

R-19 = 2900 mks rayls/m

They also added that 703 is 17324 mks rayls/m plus/minus 5%
Old 21st September 2020
Here for the gear

I received the following from technical services at Thermafiber:
The air flow resistivity of our Ultrabatt (4.0 pcf density) mineral wool is 15,700 mks Rayls/m.
This is the Owens Corning Thermafiber UltraBatt that is readily available at Home Depot in the USA. It is not the same product as Thermafiber Fire and Sound.
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