Sierra Designs Cloud 800 35F sleeping bag review: comfortable and well insulated

First impressions

Sierra Designs Cloud 800 35F tackles the chink in every sleeping bag’s armour: zippers. They add weight and bulk to a bag’s design, have a nasty habit of letting in draughts, and often jam at the worst possible moment.

Zips can also be uncomfortable, especially if you get your bag twisted around you. Which, we imagine, is why US brand Sierra Designs have come up with the unusual zipperless Cloud 800.

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In many ways, it offers the best of both worlds – the enveloping warmth of a proper footbox and a mummy-style hood in a convenient design that utilises a quilted flap. It’s basically half sleeping bag, half duvet. But this luxurious bag has good thermal efficiency too, thanks to box-wall baffles filled with 800 fill power duck down.

The bag’s fill is positioned entirely on the top and sides, with an uninsulated rear sleeve for a sleeping mat. This is designed to improve overall warmth for weight and create a bed-like structure.

In the field

We found this to be a very comfortable bag – with a couple of caveats. Firstly, the quilted flap has a 3D-sculpted shoulder pocket to keep it securely wrapped around you. This works fine as long as you like to sleep on your back but is less effective if you turn on to your side.

The design also means the hood has no drawcord to reduce heat loss, although with the quilt pulled right up to the chin this proved less of an issue. And lastly, like all bags, the Cloud 800 works best with a well-insulated sleeping mat.

However, the zoned fill means a good mat is even more important here than with most other bags. But with the right setup it does feel very warm indeed, even if the temperature drops below zero.

We liked the clever foot vent at the base too, which enables you to quickly dump heat if it gets too toasty. We were also impressed with the bag’s overall weight – despite its luxurious construction it tips the scales at under 700g. 

The pack size isn’t quite as impressive, but only because the supplied stuff sack is somewhat basic. Personally, we’d ditch it for a compression sack to really cinch down the pack size. Do that, pair it with a good mat and you’ve got a great three-season sleep system for back sleepers.