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

The Sierra Designs Cloud 800 35F sleeping bag is an innovative and versatile zipperless sleeping bag that offers luxurious comfort and delivers excellent warmth for weight

Sierra Designs Cloud 800 35F
(Image: © Sierra Designs)

Advnture Verdict

Combining the advantages of a mummy-style sleeping bag with the convenience of a quilt, this unusual zipperless bag offers both plush comfort and plenty of warmth.


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    Well ventilated


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    Comparatively bulky

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    Not ideal for side sleepers

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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.

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.


RRP: $300-320 (US)/£260 (UK)
Weight: 660g/1lb 7oz (regular) 710kg/1lb 9oz (long)
Length:198cm/78in (regular) 213cm/84in (long)
Max user height: 183cm/6ft (regular) 198cm/6ft 6in (long)
Packsize: 33x18cm/13x7in (regular) 33x18cm/13x7in (long)
Fill: 800FP DriDown duck down
Comfort: 2°C/36°F
Limit: -3°C/26°F
Compatibility: 2-season

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.

Matthew Jones

An outdoors writer and editor, Matt Jones has been testing kit in the field for nearly a decade. Having worked for both the Ramblers and the Scouts, he knows one or two things about walking and camping, and loves all things adventure, particularly long-distance backpacking, wild camping and climbing mountains – especially in Wales. He’s based in Snowdonia and last year thru-hiked the Cambrian Way, which runs for 298 miles from Cardiff to Conwy, with a total ascent of 73,700 feet – that’s nearly 2½ times the height of Everest. Follow Matt on Instagram and Twitter.