Backpacking Light Position Statement on Sleeping Bag Temperature Ratings

How did we come up with these numbers?

Due to the many variables involved, we took an empirical approach in creating this chart. We collected data from authors Hal Weiss and Ray Jardine; reputable bag manufacturers Golite, Marmot, Mammut, and Western Mountaineering; and insulation supplier Thru-Hiker. We developed our chart by compiling these figures and accounting for such effects as increased bag surface area with increased loft, and heightened “chimney-effect” convective heat loss at colder temperatures.