‘Topbags’ are perhaps a new concept for many people, but in various forms they have been around for a good few years. Essentially these bags are a normal 2-3 season sleeping bag without any insulating filling on the bottom half of the bag. This makes these bags extremely light, small and almost as warm as their ‘big bottomed’ versions when used with a good sleeping mat.

Rab actually make two topbags, the first is called the Module and does without the hood. The second is the Neutrino SL, made slightly warmer by extra filling and a trapezoidal  construction.

As I’ve outlined in previous blogs I’m a big fan of other Rab products and also Pertex Quantum which this bag is constructed from, and I had high hopes that the Neutrino SL would be the answer to some uncomfortable nights I’ve experienced on mountain marathons and other lightweight adventures.

I intially used this topbag for an Across Scotland mountain bike epic with fellow cycle touring blogger Jack Richards. In the midst of fairly warm July weather the bag performed well when teamed up with one of the new Thermarest Neo-Air  mattresses (which are superb, but more on that later!). There is a sleeve on the base of the Neutrino to allow whichever mattress you are using to be secured to the bag. In theory this is great because it prevents you rolling off your mattress or, even worse, rolling over ‘with’ your sleeping bag and exposing the uninsulated bottom to the air. In practice though, this sleeve is too small for the Neo-Air and several other mattresses which are similarly voluminous. Even when used with a typical closed-cell foam mattress, it is a fight to insert the mat as the sleeve material is grippy. Consequently, I gave up using this feature after a while. Admittedly, there are loops that allow you to string elastic in a criss-cross pattern across the base as another means of securing mats. However, having tried this on a Rab Module I still found it to be problematic. So for me as a user the mat security features on these Rab bags don’t work that well. Thermarest have their own system called the Snap-Kit which looks promising and uses poppers and self-adhesive tabs, but without trial it is hard to say whether this combined with their Haven Topbag is any better.

Since trialing this sleeping bag whilst cycling across Scotland, I have slept a further 16 nights in it on four residential trips at Adventure Aberdeen’s Cromdale Outdoor Centre. These were field camping expeditions and not hardcore ultralight challenges. For this sort of usage the Neutrino works quite well, but as we head into October I have found myself waking up five times in one night due to cold. I have been able to re-warm myself and get back to sleep but there is no doubt that a slightly heavier 700-800g ‘normal’ bag would be a more comfortable proposition.

Teamed up with every shred of clothing you are carrying on a mountain marathon, or similar venture, I am sure this bag would see most people through a night or two in the colder months of Spring and Autumn, which is a sound achievement for such a lightweight bag. However, there are a few issues which have also been present on previous Rab lightweight bags I have owned and which I would like to see resolved. Firstly, the liner and outer material of the bag are the same colour which makes the opening harder to identify in low light conditions, a point that is avoided by most other manufacturers. Secondly, the down ‘tubes’ in this bag do not hold much fill and therefore it migrates badly leaving cold spots. The best topbag I have used by Western Mountaineering has pockets of down which avoids the common migratory down problem in ultralight products. Thirdly, I am unconvinced by pertex quantum as a sleeping bag material when combined with down. While it is excellent for clothing, it does not resist damp well enough for prolonged camping.

In summary I would describe this bag as a bit muddled in execution. At 670 grams (my scales), it is not altogether that light and has some heavy additions such as a half-zip that could be exchanged for more down filling or, preferably for me, a neck baffle. It also has some functions such as the mat restraint that are at best flawed and at worst irritating. Despite this, it has some great attributes such as its ability to dry very quickly and to be packed into the smallest and highest quality waterproof rolltop stuffsac I have ever received with a sleeping bag. If the other elements of the bag were as sorted as the stuffsac Rab would be on to a winner! Would I go out and buy a Neutrino SL at £210? Yes for racing and short ultra events (but I would probably remove the mat sleeve and zip). No for extended lightweight backpacking as I honestly believe in the long run you will better served by the myriad of only slightly heavier, yet more reliable synthetics like the Ajungilak Kompakt Summer.

• RRP £210.00
• Topbag available in Shark Grey
• Suitable for male or female use
• Dealer Locator