Zpacks

A sleeping bag with no zipper at all: a sewn tube with a hood, which is the lightest way to build a closed bag and the reason the Standard/Medium comes in at 18.8 ounces for a 20-degree rating. Zpacks publishes target loft (2.5 inches for the 20 °F version) and exact shell and down weights for every one of the twenty-one size combinations, which is more transparency about construction than anyone else in this catalogue offers — and no lab rating at all, which is less transparency about temperature. Getting in and out means going through the top, and the bag cannot be vented on a warm night.

Best for: Thru-hikers who want a hood without a quilt's drafts

The Classic bag with the hood and the back panel removed — the same down weight, the same 900-fill, half an ounce lighter. That half-ounce difference is the most useful single data point on this whole site about what a hood actually costs, and the answer is: almost nothing, because the down that would be under your back has already been left out of the bag. What you are really choosing between is a hood and a draft-free back, versus the freedom to stick a leg out.

Best for: Side sleepers who move all night and want nothing pinning them