The difficulty of installing fiberglass batts is well-known in our circles. Patrick Dundon, an insulation contractor in Windsor, N.Y. stated it well: "To perform at maximum R-value, fiberglass batt insulation must be installed perfectly. It has to be of consistent density throughout the wall cavity, which means that every piece must be cut to fill the cavity completely in all three dimensions. If you can do that in every building cavity, fiberglass batts will work as labeled. But installation perfection is hard to achieve." (Q&A, May 2010).
Indeed, we've been hitting on this for a long time (see "Focus on Energy: Installing Fiberglass Batts in Stud Walls," Feb., 1993).
Allison Bailes asserts, "The problem isn't the material. The problem lies in the design and installation. Fiberglass batt insulation can work just fine in assemblies designed to make good installation possible and when installers take the time to do it right. Yes, it will cost more, but as usual, you get what you pay for."
In his recent blog post, Allison calls attention to one insulation manufacturer who has stepped up to the plate to address the challenges of getting a good insulation install. Kudos to Owens Corning, he writes, for publishing "Achieving Grade 1 with Fiberglass Batts" (PDF) and for the video below. But Allison also makes a good point in noting that there's much work left to be done, beginning with increased effort in making these materials more readily accessible to the trades.