With the arrival of winter on the hills, it’s time to add a couple of insulating layers to the rucksack, and I’ll be the first to confess that, as someone who hates being cold, the quest for the perfect toasty jacket is a particular passion of mine.

Traditionally, the choice of fillings has been between the warmth-to-weight benefits of down, or the improved resilience of a synthetic, with the latter offering improved performance when damp. Over the last couple of years, various innovations have improved on the wet weather performance of down, but this year, synthetics are fighting back, with several jackets on the market which claim to offer the lightness and feel of down, while retaining the robustness of synthetics.

Rab have two jackets in their line up  which contain a new synthetic filling from 3M called Cirrus: “a new, breakthrough insulation which combines almost all the key benefits of natural down and synthetic fillings, whilst avoiding their limitations”. The Nebula is the warmer of the two offerings, weighing in at 560g for a Large. It’s a neatly tailored jacket, managing to be neatly shaped to the body, while still retaining enough room to fit several layers underneath. It’s a bit of a tight squeeze to fit it under my usual winter hardshell, but the cut and weight suggest that the Nebula is intended as an ‘overlayering’ piece.

I’ve been wearing it for a few weeks now, but the arrival of snow on Ben Lomond gave me the opportunity to give it a more thorough test in the sort of conditions it’s intended for. There’s no obvious objective point of reference to compare 3M Cirrus as an insulating material with the more commonly used materials such as the various iterations of Primaloft, but my initial impressions are that it compares favourably in terms of the warmth to weight ratio. There was a stiff breeze to ramp up the windchill when I stopped to take the photo at the top of the review, enough to limit the dexterity in my fingers by the time I had the camera set up, but the Nebula kept me comfortably warm over the top of a light base layer and pull on fleece – I’d go as far as to use the term “toasty”.

As an experiment, I left it on as I made my way up the last third of the Ptarmigan Ridge to the summit of Ben Lomond, where I took some more photos, then down the main path. Moving at a moderate pace, I found the Nebula comfortable whether on the move or stopped. One of the traditional benefits of down is that it feels comfortable to wear across a wider range of temperatures than synthetics, which tend to feel sweaty sooner than down; I was interested to note that the Nebula felt more like down in this respect.

The Nebula has a fairly beefy Pertex Endurance outer shell, which does limit the draping effect associated with down – the upside of this is of course better abrasion resistance. The hood is up to Rab’s usual high standard, with enough volume to fit over a helmet and give good protection at the sides of the face. I love the length of the jacket, particularly the dropped rear hem,  which together with the voluminous hood, gives a reassuring sense of being ‘wrapped up’ when wearing it. Water resistance wasn’t really tested, with only a few light showers of snow, but the jacket brushed those off easily enough.

Initial verdict – it’s a keeper, and definitely a good option if you’re looking for a medium weight insulating jacket this winter.

Price: £160

Weight: 580g (L)

Materials: Pertex® Endurance® outer fabric / Cirrus™ powered by 3M Featherless insulation

Website: https://rab.equipment/uk/shop/new-for-winter-15/nebula-jacket-30