Problems installing cotton insulation

I bought some Ultratouch cotton fiber insulation a few months ago thinking that it would be a great natural product for the cabin I am building. This is the stuff that comes in blue unfaced batts, and is often said to use recycled blue jeans, although it uses pre-consumer denim from factory waste. I bought it from a (great) Brattleboro, Vermont retailer Renew Building Materials and Salvage for for 88 cents a square foot. Unfortunately they ship it from Arizona but it seemed worth the effort. Within a couple hours of working with it, however, I was ready to abandon it in favor of blown-in cellulose, and returned all of the unopened bags minus a restocking fee. What went wrong? Three things.

• It's too thin
• It's too wide
• It's hard to cut

The worst flaw of the product is that it is too thin. I bought the R-13 batts that are supposed to be 3.5 inches thick to fill the stud cavities in a standard 2x4 stick-frame wall. Just like the fiberglass insulation I've worked with in the past, the batts were compressed into a bag for shipping. You are supposed to be able to take them out of the package and they will "fluff up" to full size in a process called "loft rebound." However, as the photo above shows, that never happened. The actual thickness varies. At best it's three inches; at worst it's less than two. This photo, by the way, is taken after the batt has been sitting out, uncompressed, for six full months. It did all of its "fluffing" in the first few hours and hasn't improved since. What's wrong with that if it's R-13? Well, it's not really R-13. The air pockets provide the insulation, not the cotton. If you take the same cotton and compress it into a smaller space, there are fewer air pockets and thus less R-value, as the cotton conducts more heat. That R-13 value is based on 3.5 inches of fluffy cotton with lots of airspaces, not two inches. Also, since the batts are so thin, they leave about half the stud cavity open. That massive air cavity (which remember, I already paid 88 cents per square foot to fill) provides ample room for air currents to move, sucking out heat and bringing in cold air, worsening the total R-value of the wall even further. The people I bought it from at Renew were concerned. They noted that the larger R-19 batts seemed to fluff up better. They encouraged me to give my feedback to Ultratouch. When I asked the Ultratouch reps about this problem they told me that they haven't had such problems. Secondly, it's too wide. According to Bonded Logic, the makers of Ultratouch, this is a feature, not a bug. To quote the website: "UltraTouch is manufactured in oversized widths to ensure a tight friction fit and fill capacity." Indeed, the insulation I bought is a full 16 inches wide. Meanwhile, the standard 16-inch on-center stick-frame wall that I had built has a stud cavity that is 14.5 inches wide. So a full 1.5 inches of the stuff is added on for a "friction fit." I wasn't expecting this when I opened the package, but I was willing to give it a try. In practice, I would say that a 1/4-inch of extra width would be enough to provide the friction fit. So what happens to the additional inch-and-a-quarter? It gets squeezed into the corners. You then have two problems. One is that the batt balloons out a little to the front, creating a significant airspace behind it. Two is that the insulation on the edges gets compressed, reducing its R-value. That also rounds the corners of the insulation, and since the stud cavity is rectangular, not rounded, it adds air gaps running all the way up and down, creating convection and further reducing thermal performance. You can see both effects taking place in this photo:

Again, Bonded Logic insist that this is not a problem. At Greenbuild last year, the reps told me that it worked for them when they installed it. Curious, I came back to their booth at the recent AIA National Convention in Boston to research the issue further. The Ultratouch booth features a gorgeous stick-frame wall with batts of Ultratouch installed, looking perfect and also, strangely unattainable.

So how'd they do it? Using a tape measure from the Lafarge booth down the row (thanks!), I measured the wall and found that the official Ultratouch mockup uses 17-inch on-center construction. This allows an extra inch to accommodate the wide batts.

Wacky! But clearly these guys knew what they were doing. My question is--why haven't they told the rest of us? Knowing what I know now, if I were to use this product again, I would either use a nonstandard framing technique such as 17-inch-o.c. walls like Ultratouch did, or I would rip every single piece lengthwise to attain a more exact fit. But -- and this offers a good segue into my third point -- the stuff is really hard to cut. Treating it like fiberglass, foam, or many other types of insulation that can be cut with a utility knife will give you a shredded, uneven end -- see the lower end in the photo. (Tearing it by hand, as Peter Yost and Nadav Malin here at Environmental Building News found they had to do when they reviewed the product eight years ago, works somewhat better, although it generates a lot of dust. Peter also noted the same problem with loft rebound in that article. It would be great to to into his attic to check on that now.)

Bonded Logic recommends the Insul-Knife made by Cepco Tool Company to cut it instead. I acquired one of these and found that it's a really nifty tool that has all kinds of uses. Cutting cotton batts is not one of them. It does create a satisfactory cut when it's really sharp -- see the upper end in the photo (above). But it requires a lot of elbow grease, and it dulls within a few cuts and requires sharpening. Also, it works best on crosscuts, and is not very practical when it comes to getting a long, straight rip.

Bonded Logic recognizes this, apparently, because they also recommend a Bosch Foam Rubber Cutter as a motorized cutter. I wasn't that interested in buying a specialized power tool just for installing insulation. If I were doing a large commercial job, however, I imagine that this would work well and probably wouldn't take much longer than cutting fiberglass, at least until you factor in the ripping. For the several pieces that I did install, I found that a tablesaw worked best for long cuts, and a circular saw worked reasonably well for crosscuts. I have talked to other residential installers and found that people who stick with the product find a motorized system that works for them using standard tools. I might have done so if not for the product being too thin. As I stood there in my freezing cabin last winter (which wasn't getting warmer very quickly with the problems I was having with Ultratouch), I thought about setting up a motorized cutting system with tools on hand, and ripping every single piece. But I realized that I could do all that and still not get the thermal performance that I had paid for because of the lack of "fluff." I was already planning to blow cellulose into the ceiling so I decided to do the walls as well. Have you installed cotton insulation? How did it work for you? I do have some good news to report from my search for the ideal way to cut Ultratouch. I came across the Olfa 45-mm rotary cutter. While this didn't work for Ultratouch, I love using it on materials like burlap, housewrap, and red-rosin paper--provided that I am cutting on top of a hard surface. Because it rolls and avoids thus avoids catching on things, it works much better than a utility knife in some applications. Replacement blades are spendy, though.