Purchased in 2007 for an expedition trek cmping on a glacier (Baltoro to K2) where the rivers froze at night it kept me warm. 10 years later (it had been used in between) in Ladakh it still did the job masterfully, this was a winter trip where the average night temperatures where and when we camped are reputed to be -25c, I wore clothes in side the bag but remained warm, someone was heard to complain his wet wiped had frozen solid, as had my 'hot' water bottle..it is bulky and heavy so if you arent carrying it this is the one to get, also being synthetic it doesnt soak up moisture like down filling