Thermarest Hyperion 32F/0C sleeping bag review: positively luxurious

First impressions

The Thermarest Hyperion 32F/0C sleeping bag will be a welcome release to fans of the brand. Though they’re best known for their superb sleeping mats, US brand Thermarest also make a wide range of sleeping bags and quilts, specialising in lightweight down for backpacking and thru-hiking. The Hyperion 32 is one of the brand’s flagship bags, and on paper the specs are impressive.

It weighs in at just 460g/1lb in total, of which 250g/9oz is made up of premium 900 fill power hydrophobic goose down – that’s pretty much as good as it gets unless you turn to very niche (and very expensive) ultralight manufacturers.

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Aside from the fill, the bag is made up of a lightweight 10-denier ripstop nylon shell, with internal box-wall baffles that have internal mesh side walls to save weight. Most of the down – 70%, in fact – is placed on the top and sides of the bag, leaving your mat to insulate you from beneath.

It’s an obvious solution given the brand’s expertise when it comes to sleep systems, meaning this bag would pair perfectly with a lightweight insulated air mat like the Thermarest NeoAir Xtherm or the Uberlite.

In the field

The first thing to note is that, packed in its stuff sack, this sleeping bag is tiny. It would merit a place in even the most weight-conscious hiker’s pack. We easily stashed it in a 40-litre rucksack ready for a cheeky overnighter in central Snowdonia. That makes it perfect for fast and light adventures, whether you’re running a mountain marathon or fastpacking a long-distance trail.

But unlike many ultralight bags, the Hyperion is positively luxurious. When you shake out the bag, it lofts beautifully, inviting you to climb straight in. The fabrics have an extremely soft handle that also gives superb next-to-skin comfort. As a result, we slept very well indeed and even found the unusual design with its zoned fill to be highly effective – provided you don’t twist the bag around.

To prevent this, the bag has thin (i.e. delicate) elastic straps on the underside that slide beneath your mat. Fortunately, the overall fit isn’t too restrictive, so turning inside the bag to sleep on your side is easy to do. In fact, the only element that is slightly awkward is the lack of a full-length zip, which means you need to do a bit of wriggling to get in and out.

On the other hand, this half-zip design minimises heat loss and saves weight, which are arguably more important considerations. In terms of warmth, our experience with the Hyperion 32 was that met its stated temperature range, and with an insulated three-to-four season mat (i.e. one with an R-value of at least 4.0), it proved comfortable down to freezing point.