i've used the endurance in good weather in late spring/early summer. they call it the "endurance bag cover" because that's basically what it is. no zippers or mesh or anything. but yeah, it is LIGHT and SMALL. also, the endurance is not going to breathe very well but just depends what you want/need it for in the end. i'm looking for something a little beefier that i wouldn't mind being cooped up in on top of rainier but will also be useful for just about anything else i could possibly want to do with it. (and hey, why are stuff sacks *always* too small for the stuff they're supposed to get stuffed with anyway?)