We bought a batch of the "ultralight" bags to use for Pacific
Crest Outward Bound about 10 or 12 years ago. The worked comparably
in warmth, weight, and durability to the 20 degree, $60, slumberjack synthetic bags also used at the time. By the end of the summer with daily use and monthly laundering they had lost roughly 1/3 of their loft and students were getting cold at below freezing temps.