Sierra Designs has pioneered innovative zipless bag designs, including the Nightcap 20 sleeping bag which is part of our guide to the Best three-season sleeping bags for hiking. There’s isn’t any weight saving by losing the zip, as lots more insulation is needed to create the wrapover shape, but it does create versatility for warm sleepers who like to be able to vent through the night and allows for spreading out a bit if needed. There’s even an overlapping opening at the feet for dumping heat. The drawback is if you are an energetic side sleeper: the wrapover comforter can fall open with too much movement, leading to draughts.

Price: £160 | Weight: 1626g | Fill: 1276g recycled Sierraloft Eco Synthetic | Shell: 20D recycled polyester Construction: synthetic fill | Zip: none | Length: 188cm | Rating: comfort +1°C, limit -5°C | Sizes: one | Men’s version: yes

The big plus with the Nightcap 20 is that it’s wonderfully easy to get in and out of, and there’s no danger of snagging zips. The bag includes a sleeping mat sleeve on the base that you can slide your pad into to keep it in place. There isn’t a neck baffle, but the comforter can be tucked in and around the shoulders and works well if you don’t move about too much. 

It’s a fairly heavy bag at 1626g but the fill is quite compressible for synthetic insulation, and the bag can be squished down to much less than it’s advertised 19x38cm. The Eco Synthetic fill is made from recycled water bottles, and the shell
is recycled too. 

Overall, it’s clever and warm, with a smaller environmental footprint than many other synthetic bags; and although it won’t suit everybody, some will love the versatile comforter system.