It took a little while to find, but here is some info:
"For example, ORNL researchers have determined that some types of blown-in insulation in buildings in the northern United States permit air movement within the insulation, resulting in natural convection. Compared with conduction, convection allows more heat to escape from within a building to the outside. The researchers confirmed that natural convective heat loss in some loosefill fiberglass insulations can be responsible for as much as half of the heat loss at very low temperatures."
ORNL Review Vol. 25, Nos. 3 and 4, 2002
http://www.ornl.gov/info/ornlreview/...t/usemain.html
I'm looking for the original data, but the study is old enough that it might not be online.
Tim