Extreamly light, packs bery small and very, very warm when used with a thick air pad like a thermorest neoair. Use it as directed as a part of a sleep system and its exactly as advertised. You do need to keep it well sealed and tucked under your sleep pad with no gaps for it to really keep you warm. Best use for me was a late summer solo trip in the White Mountains where it dipped into the low 40'
This review was written in the old system and had content requirements that are different than reviews written today.