Rab Solar Ultra 1 Sleeping Bag Review

The Rab Solar Ultra 1 is part of Rab’s high performance synthetic sleeping bag range. Using recycled Stratus insulation along with Rab’s TILT heat reflecting technology the Solar Ultra 1 is an attractive proposition for those who may wish to eschew down either on ethical grounds or because wet/damp conditions would make down a poor choice. Alongside the recycled insulation the recycled Atmos shell fabric and the fact that the Solar Ultra 1 is also certified as being fluorocarbon free will also appeal to those looking for a sustainable ‘eco friendly’ sleeping bag. Rab themselves are moving toward a ‘Net Zero‘ target by 2030 which together with Fair Wear accreditation make their products a sound environmental and ethical choice for most people.

I have been a long time down sleeping bag user and advocate – warm, light and long lasting. The only fly in the ointment is their disastrous performance in the wet. I’ve had two brief forays into the synthetic world; firstly with a very thin ‘reflective’ synthetic mountain marathon bag purchased at the Saunders mountain marathon in the early 90s which was useful for passing kit checks and little else! Secondly is a PHD over bag, insulated with Thinsulate which works well to boost and protect a light down bag but is generally too bulky to take on ‘light weight alpine’ style bivis. Generally I preferred down bags for their unbeatable warmth to weight and compressibility ratio but have always used dry bags to guard against getting them wet in transit together with bivi bags, careful perusal of the forecast and a little prayer when bivi-ing out. However like most things technology has been moving forward apace and I’ve long been a fan of synthetic insulation in belay jackets as there’s no way to keep them dry in Scotland (or many other places) in iffy conditions so it seems the time is right to give synthetic a real try.

Rab have long been at the forefront of down sleeping bag and clothing design so they know a thing or two about insulation. additionally being UK based they know a bit about wet/damp conditions. Their Alpine Generator belay jacket that I reviewed last year is an excellent example of this. When the Solar Ultra 1 arrived I was pleasantly surprised at how soft and ‘down like’ it felt in the hand. Compared to a similar down bag from Rab like the Alpine 400 weight and compressibility were not too dissimilar; Rab lists the Alpine 400 -5°C as 840g and fitting in 35X20cm stuff sac whilst the Solar Ultra 1 -4°C 880g and fitting in the same 35X20cm stuff sac. The Solar Ultra 1 actually weighs 952g on my scales but it does easily fit in the provided stuff sac – always an important factor when packing up half awake from a bivi. I would suspect the Alpine 400 would compress a little better ultimately and it is rated a little warmer but there is clearly not a yawning chasm between the two performance, weight and compressibility wise. In terms of features and design there is a lot going on with the Solar Ultra 1.

First off this is a bag that has been designed with sustainability and minimising environmental impacts from the get go. Both the insulation, the outer and the lining material are composed of recycled fabrics. The insulation is augmented by what Rab terms TILT technology (Thermo Ionic Lining Technology) which is a reflective coating applied to a polyester scrim between the liner and the first layer of insulation that acts a little like a space blanket reflecting back radiated heat whilst still remaining breathable. Certainly this treatment doesn’t impede breathability a this was a very comfortable bag even in very warm conditions with none of the ‘clammy’ feeling I associate with synthetic bags. The synthetic Stratus insulation is used in a similar way to a differential fill down bag with two layers on the upper, where it does most good and a single layer on the base, where it would be compressed and hopefully your ground mat will insulate you. The upper quilting is offset from the elasticated inner quilting which helps eliminate cold spots. The Solar Ultra 1 also feature a performance mummy cut, neck baffle and suitably snug hood and a dinky little pocket to store your watch/phone in so you don’t loose it in the tent/bivi/van chaos + you get to hear that alpine alarm! All versions of the Solar Ultra 1 have a left zip (so no zipping together two bags) with an anti-snag puller which is about 95% effective. The provided compression sac is a sensible size in that it is easy to stuff the bag in fully without a fight and even when fully compressed it still has a bit of ‘squish’ left to get it into the bottom of the sac.

In Use
In brief the Solar Ultra 1 has been outstanding. Ultimately premium down bags will still have the edge at the top end in terms of the weight/compression/warmth equation but the Solar Ultra 1 is getting pretty close. Close enough in fact that if there is much chance of damp then I would choose it over a down bag without hesitation. Once you get into the serious sub zero temperatures then things are still perhaps in down’s favour. However when the temperatures are around zero the Solar Ultra 1 is a compelling choice. It fits easily into a 30litre alpine sac with room to spare for stove, food, water, clothing and rack. You may even choose to skip the bivi bag with a good forecast (obviously still keeping your reflective survival bag tucked down the back panel of the sac for emergencies). Used for general valley camping in the van it was perfectly comfortable with the zip fully open even on warm nights.

Chercheurs d’or Bivi

A bivi at around 1970m in the Aiguille Rouge was toasty warm and the robust Atmos face fabric meant I didn’t need to ‘baby’ the bag if I ended up shuffling around on the rocks. Comfort, performance and compressibility are all at a level that make the Solar Ultra 1 a serious contender for most summer alpine use, and beyond if supplemented with your belay jacket etc. The performance of the synthetic fill means that damp is gong to be a negligible issue, if you get wet anything is miserable but at least with a synthetic bag you have a chance of drying it out! Once upon a time there was pretty much no decision to be made in the down vs synthetic sleeping bag competition. It was always down if you needed to carry it on a climb just in terms of weight/warmth/volume issue. The arrival of proofed down even helped negate some of that progressive damp induced performance decline if you were in a tent for several days unable to air out your bag. With the arrival of modern synthetic bags like the Solar Ultra 1 there is going to be less of a clear cut answer. They offer perfectly usable temperature/volume/weight metrics with massively better damp performance. The down bags will still win out longevity wise and even though the synthetics are initially cheaper as a long term investment down would win out if looked after. On the subject of longevity, if you put a hole in your down bag (as a friend did once whilst bivi-ing) and don’t notice you’ll loose a whole chambers worth of down something that is not an issue with a synthetic fill bag!

Overall I can wholeheartedly recommend the Solar Ultra 1 and though its not currently part of the Rab Rental scheme which is a shame the Solar Ultra 3 is so you could give that a try for a little as £17 for a three days. The Solar Ultra range covers the Solar Ultra 1 at -4°C, Solar Ultra 2 at -10°C (1140g) and Solar Ultra 3 at -13°C (1360g). The Solar Ultra 2 and 3 are also available as a women’s model with a women’s specific cut, wider at the hips/narrower at the shoulder.


  • Compressibility
  • Lightweight (for synthetic at this temperature rating)
  • Robust
  • Useful features
  • Damp conditions performance


  • Probably longevity compared to down
  • Marginally overweight compared to published specs

SRP £190


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