This is my new favourite synthetic sleeping bag - snug, well-designed, and not overly heavy for backpacking and general outdoor use.

Deuter's Exosphere range covers several models, 0º -6º and -10º, each available in standard size or slimline (initialled SL). As a bag for UK use in summer through to the bridge seasons, I've been using the Exosphere 0º SL, which fits people up to 175cm tall; the standard length Exosphere is 185cm, while in the -6º model only there's also a version at 200cm. All feature a snazzy elasticated construction, which I'll come onto below.

Warmth

The model numbers of course refer to the temperature rating of the bags - specifically the 'lower limit', which is the temperature at which a 'standard man' (if there is such a person) can sleep for eight hours in a curled position without waking. On average women tend to sleep colder, but on the other hand anyone's experience of a sleeping bag's warmth is also going to be influenced by factors other than gender, such as how well fed they are, how tired they might be, what they're wearing inside the bag and how draughty the tent is.

The Slim Line versions are designed as women's bags, which have a different shape to the standard models for a closer fit that eliminates cold spots. The addition of fleece inserts around the kidney and foot area for added warmth goes some way to making up for the fact that women tend to feel the cold more at night.

It's worth noting that the 'comfort limit' of the 0º SL, namely the temperature at which a standard woman can expect to sleep comfortably in a relaxed position, is only 5º. I would take the 0º lower rating of my bag as a rough guide to lower limits, and I definitely wouldn't plan to go much below freezing in it. I have not experienced it yet during real cold spells, but it has certainly done its job in our changing - and not always very warm - Scottish summer weather. I think it's snug enough to take out in kinder spring and autumn conditions too, even up high, without being too worried.

Weight and packability

If you're very focused on going ultralight, then this isn't for you. At over 1kg this synthetic-filled bag is a lot heavier for its insulating performance than the best lightweight down-filled alternatives. Indeed one down model of equivalent temperature rating, reviewed last year on UKH/UKC, weighs less than half as much as the Exosphere 0º SL. But still, I don't think the weight is excessive for a synthetic bag, and it's not been enough to worry me in a rucksack. It comes with its own compression sack and packs down really neatly for backpacking and bikepacking - I find it less bulky than other synthetic bags I've used.

It is worth noting that the longer version of the Exosphere -10º weighs a massive 1785g, plus a further 100g for the stuff sack, so if you're looking for a winter/alpine bag and weight is an issue then at the thicker/warmer end of the range you might want to start thinking seriously about down-filled alternatives.

Fill

For the insulation Deuter have used something called Thermo ProLoft, a blend of hollow and solid synthetic fibres. The idea is to give you an optimum balance of warmth/weight, compressibility and durability. For a synthetic fill there's a good amount of loft here, and the bag does pack down small too, so the Thermo ProLoft seems to be doing its job. Unlike many down bags, I've had no fill leakage with the Exosphere, and overall it feels like a bag you don't have to treat with real care. For UK use, the obvious advantage of synthetic fills are that they tend to maintain their performance better than down when things get a bit damp. The other clear bonus is price: at £145, this sleeping bag is a lot more affordable than most down bags of similar warmth.

Fabric

The outer fabric is a 30D nylon, which feels durable enough for a sleeping bag, and quick-drying too. For added wet weather peace of mind there's a patch of water-repellent fabric at both ends of the bag, where your head or feet might nudge up against the inner of a tent - and as I spend a fair bit of time camping in the Highlands, in a one-person tent, I think this is an excellent feature. And well done to Deuter for using PFC-free fabrics here.

Inside you get areas of fleecy lining around the middle of the body and down at the toes, and thanks to these the bag feels warm as soon as you get into it - a nice luxurious touch.

Design

As I mentioned in the intro, all the models in the Exosphere range feature stretchy walls. These are designed to bring the fit in close to the body, to help reduce cold space, while still allowing plenty of room to move around and get comfy. Deuter aren't the only ones doing this, but you wonder why all sleeping bags don't have a bit of stretch since it clearly helps both in terms of comfort and snugness.

For valuables, torch etc there's a wee secret pocket inside. The zip has an anti-snag baffle, and you can open the bag right up from the toe if ventilation is needed. For couples, or close friends, it's also possible to connect two bags together.

A nice foot-shaped toe area, and an effective hood section, complete this really well-designed sleeping bag.

Maybe the colour should not matter so much but that bright lining certainly makes me feel happy and warm in my wee tent!

Deuter say:

The freshly revised, detailed ergonomic cut of the hood and the foot section brings our technical synthetic sleeping bags to perfection. the high-tech construction with its internal and external elastic chamber seams still provides a 25% expansion in width. This brings the insulation close to the body, eliminating cold spots, yet guaranteeing comfortable freedom of movement.

• Weight: 1060g + 80g stuff sack
• Fill: Deuter Thermo ProLoft
• Inner Lining: 30D Nylon Taffeta
• Outer Lining: Durable, breathable, quick drying 30D Nylon
• Pack-Size: 16 x 32cm
• Bodysize: 175cm Exosphere 0C SL; 185cm Exosphere 0C
• Separate drawcords on the ergonomically shaped hood for precise adjustment
• New, ergonomically shaped foot section perfectly adapted to the natural foot posture, extra insulation section for added warmth
• Dryzone at the head and feet protect from moisture with a water repellent shell fabric
• Body-warmer fleece inserts made from fluffy brushed Thermo Fleece keep the kidney zones, top and bottom and the foot zone warm in the SL versions
• Full-length, two-way YKK zip (coupleable)
• Anti-catch baffle with extra reinforcement
• Internal valuables pocket
• Full compression stuff sack

For more info see deutergb.co.uk