Fiberglass insulation R Factor change?

Thanks. Waiting to hear from J-M. My thinking is that by reducing the size of the open cells, has to have some effect. Will it? If so, What? That's the question.

Worse. Go to Owens-Corning.

Thanks. The return answers are mixed, but I think you're right. Incidentally, I've tried J-M and haven't heard, as yet

Mixed? Two of us answered. We both say it lowers the R value.

BTW, go to Owens-Corning as I suggested. They publish a compression chart that will exactly answer your question. Johns-Manville may have such a chart also.

Will do (OWENS-CORNING chart). Thanks again.

The "mix" I mentioned, pertained to home and office building engineers that I've spoken, too. That's what prompted my posting. In almost all cases, including a guy from J-M were guessing! Not all were wrong, therefore, had to know.

This will take you to the link that TVP45 was referring to.

http://www.owenscorning.com/around/insulation/faq_general.asp

At the bottom of the page you will find that the rating table that I was talking about, if you're stuck with 2 inches there may be better materials available than fiberglass. A look at the table will show that a rating of R13 drops 6.6 when compressed into a 1 1/2 inch space (common 2 by 2) of course if you're stuck with a 2 inch space you can't get any better rating with fiberglass, hopefully you're just using this for reference, if so this table should be helpful in deciding what material thickness is best for you.

TVP45 was answered and I will follow up on your's and his lead.

The original question/answer prompts this next one: If negative (reduced R factor), would finer diameter fibers having a matting of 2" or 3" thick have the same R-13 factor as 4" stuff? (Cost savings) The only obvious answer that comes to me is that J-M & O-C have already considered this, since other issues may be involved. Such as: they can't make the production rate fibers fine enough, or cell size requiremnets can't be met by having smaller diameter fibers.

These are only my quesses and I wonder if any are on the mark.

Thanks again.

A thought experiment, why didn't you say so. I think you're on the mark, there may not be much room left for improvement with conventional fiberglass. I went website hopping this afternoon and found a good link. The author explains the subject in reasonable detail.

http://composite.about.com/od/aboutglass/l/aa980630.htm

Aerogel's were mentioned in this link . A quick look at the Winnipeg online encyclopedia revealed a complete list of R values per inch of insulation. Conventional fiberglass averaged about 2.2 .I believe aerogel at R 10 per inch was the best insulator.

Let me know who wins the argument at the office.

The R factor on the insulation reflects its insulation properties in a give space. Since you have reduce the space in the wall to 2" you have already reduce the R factor of the wall greatly. To cram insulation made for an 4" wall tightly into a smaller space will reduce its insulating properties. Insulation is made to deaden air flow off the surface. If pack tighter the insulation material becomes the conductor. The rate depends on the type of insulation.

The warm air against the inner wall rises to the top cooling against the outer wall and dropping to the bottom them warming and rising again against the inner wall. This starts a circular effect of air movement. Insulation slows the air movement. If packed too tight then the fibers conduct straight thru from inner to outer.

Interesting! If the air flow conditions is vertical as you've discribed, that makes sense to me! I've always assumed that the cold, dead air flows in a horizontal direction, which is then entrapped by the vast amount of cells, making it unable to cool down the inner wall.

I've got to rethink this out. That information is most helpful. Thanks for that.

So, give YWRoadRunner a "Good Answer" He got it 100% right in the no. 1 post.

Good answer. You're right. Ozzb was on the mark also.

Happy new year, from what I have learned about insulation ratings, is with fiberglass, it is not the thickness, it is the airgap that provides the insulation barrier. If you take for example, 6 inch insulation compressed to 2 inches, you lose the vapor barrier and R factor, that is why roofs are generally R 30. tho help contain enegy loss or absorption.

Hope this helps

In general, the answer would be worse, but I read years ago about a .1" thick insulation used on space craft with a factor of R-21.

The fiber glass insulation was sandwiched between two reflective metalized mylar sheets,sealed, and the air evacuated out. Sort of like a vacuum Thermos or Dewar flask.

Not necessarily a practical thing, but neat!

Thanks for that. With lots of you guys "kicking-in", I've learned a lot. RE space craft, 1" thick insulation may have been the aerogel that one of the writers talked about. As a matter of fact, I'm waiting to hear back from the 'aerogel' makers. Just curious.

From all of the infrmation that's come in and data chart, I'm now convinced that compressing insulation reduces the R factor, mainly because of the open cell air movement. However, styrofoam is a closed cell material, which is also a good insulator, 'but can't take heat.'

Thanks again.

You have gotten great answers here, I just want to add a few ideas or alternatives.

If you are stuck with tight spaces, the normal "home depot" r11 stuff won't do. The common insulation has an r11 or r13, and a rating of r19 is achieved by doubling the thickness.

alternatives include mineral wool, or denser inorganic glass fibers such as Owens Corning 703.

A 2" piece of 703 has an r rating of 8.6 where your standard r11-13 comes in an average thickness of 3 1/2". Once you compress it to 2", you may lower your r rating enough where it may wise to use other materials.

Also, I use these materials constantly in my business ( www.csoulpro.com ), because they provide superior acoustical properties, utilizing an "STC" rating (sound transmission class).

Link: http://www.owenscorning.com/quietzonepro/pdfs/NoiseControlDesignGuide.pdf#xml=http://ocsearch01.oc.iscgnet.com/texis/search/pdfhi.txt?query=703+stc&pr=www.owenscorning.com&prox=page&rorder=500&rprox=500&rdfreq=500&rwfreq=500&rlead=500&sufs=0&order=r&cq=&id=474686e772

the R-value would be worse. any time you compress insulation in any way the R-value per inch goes down