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Has the Oak Ridge study on convective heat loss in blown fiberglass been updated to cover newer materials?

I'm evaluating blown cellulose vs. blown fiberglass (Knauf Ecofill). The Oak Ridge study is often quoted regarding the drop in R-value of blown fiberglass when the temperature differential is high. However the tested fiberglass density (.4 - 5 lb/ft^3) is much lower than the newer fiberglass. Also, for what it's worth (maybe nothing), Knauf states that "When tested against three cellulose products using ASTM C 522, EcoFill Wx showed 20 to 100% better air flow resistance than three leading brands." That's an acoustic test, though, maybe not applicable to convection.

Anyway, the bottom line is: has anyone updated the ORNL test with newer blown fiberglass? The ORNL site itself doesn't seem to mention that test anymore, and says nothing bad about blown fiberglass in its various insulation-related papers.

Asked by Neil Weinstock
Posted Jul 21, 2014 9:51 PM ET


6 Answers

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The last time I researched this issue, I learned that newer varieties of blown-in fiberglass resist convection better than the older varieties. But since the source of the information was fiberglass manufacturers, I concluded (like you) that the issue isn't really settled.

If you have access to cellulose, that is the material to specify. If you are located in a region of the country where (for mysterious reasons) insulation contractors don't yet offer cellulose, you may be stuck with blown-in fiberglass. If that is the case, add an extra 6 or 8 inches to make up for the fact that it may not perform as well as cellulose.

Answered by Martin Holladay
Posted Jul 22, 2014 4:34 AM ET
Edited Jul 22, 2014 4:36 AM ET.


Hello, I am Director of Product Affairs at Knauf Insulation. The study you reference is very old. The study lead to a few products increasing thickness to make-up for the deficiency. Knauf products were not impacted. Our label is very accuarte and 3rd party verified. It works and works well. NAIMA studies with NAHB show no R-Value loss after 5 years and 10 years time period. Certainly cellulose interests can not say that. With deference to Mr. Holladay's regard for glass fiber and its manufacturers....we are proud to be one. My contact information is 317-421-8704 should you have techncial questions I would be more than happy to answer them for you.

Answered by Scott Miller
Posted Jul 22, 2014 9:06 AM ET


Scott: The (required to be accurate to be legal) 3rd party verified labeled R is an ASTM C518 test, a test which the test fixture itself provides both top & bottom air barriers, and is performed over a limited temperature delta. The testing required for labeling will never show convective losses of performance associated with open-blown material in an attic where there is no top side air barrier when the bottom side is the warmer than the attic air.

If there are published NAIMA & NAHB or other in-situ /other studies that demonstrate the product performs at the labeled R (at real-world cold climate delta-Ts) even without the presence of a top side air barrier, it would be useful to have them published on the web, and point us to them. Even a writeup real data on the ASTM C522 testing mentioned by Neil would be useful- which products were tested, at what density, and what the hard data indicated. Simply alleging the existence of some test somebody did somewhere demonstrating some outcome isn't very satisfactory without the particulars and the hard numbers.

If the material really IS superior in an open blown attic application it's worth putting up the evidence rather than vaguely referencing the testing. Don't be shy about it, and don't make people call you to chat about it on the phone- PUBLISH the test methods & data to get a fair hearing of th evidence.

Fairness may not always fall in your favor, but unsubstantiated assertions (verbal or blogged about) don't really cut it, given the less than sterling history of performance claims within the insulation industry as a whole. If you're truly "...happy to answer..." the technical questions, doing it by private telephone conversation isn't the way to get the word out. (Just sayin'...)

Answered by Dana Dorsett
Posted Jul 22, 2014 4:40 PM ET


Hello Martin,
I'd like to refer you to our technical bulletin on convection in fibrous attic insulation. IST09-005. It can be found here:

Granted this is not third-party data, but I was personally involved in the research using C1373 not C518) and we presented it at ASHRAE in 2009. Essentially, Johns Manville responded to the ORNL study by redesigning the product.

I'd be glad to discuss it at greater length.

Answered by Diana Fisler
Posted Sep 17, 2014 5:37 PM ET


Thanks for your comments, and for providing a link to the interesting document.

Answered by Martin Holladay
Posted Sep 17, 2014 6:29 PM ET


Dana said it well. Lets see the attic initial test plan and test set-up, approved test procedure, test instrumentation, models, pictures of the test in several stages, and the final test report including values from all thermocouples, pressure gages, humid-stats, locations, and any other instruments. Provide the number of the third party Project Engineer or Test Engineer. There are a few out here that have plenty of experience interpreting test data, that is what makes GBA so unique :) Requesting private party chats that may or not have this experience is already flawed and we have not even seen the data yet.

Answered by Terry Lee
Posted Sep 17, 2014 7:28 PM ET
Edited Sep 17, 2014 7:35 PM ET.

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