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The biggest drawback for me is how slippery the material is. There's a lot of sliding around even despite the two attachment loops. I often have to make adjustments through the night, esp. when sleeping on a small incline (and most of the nights there's one, since out in the wild it's hard to find an absolutely flat spot for a tent).
I purchased this elsewhere but the review applies to wherever thermarest sells.
The Hyperion 32 is an excellent bag. It’s weight can’t be beat.
The construction is superior but there is a design flaw. I gave the bag three stars because of the zipper and draft tube placement. It is clear that the bag is made for those who sleep on their backs. As for reality that doesn’t happen. I tend to move and the only way I could be fully comfortable, and not get a cold spot along the zipper, was to stuff my down jacket along the zipper. I didn’t have any issues with the right side of the bag so it wasn’t the strategically placed down. The draft tube is on the top. Cold goes down. So it’s placement, on the top of the zipper, I feel, is a design flaw. But I’m still thinking that wouldn’t make a difference and a different zipper would. I know for sure it was the zipper because it felt cold and the bag did not. The coldest it got was 35° and that was only one night as the other nights, 5, were 40-45° I do not consider this a 32° bag when I get a draft at 42° and I run hot so I love cold weather. I shouldn’t have to wear fleece, or stuff a down coat, to be comfortable in a bag that’s rated 42° for comfort.
I would rather use my Cat’s Meow from 1996. That is a 30° bag with primaloft and is good at 30°. It’s the only bag I’ve had that’s rated for 30° that isn’t freezing at it’s temp rating. Yes, I know bags are rated differently now.
The only reason I wanted this bag is because I can drop a pound.