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The Rab Alpha Flash jacket is an extremely lightweight and simple mid-layer fleece made entirely from Polartec® Alpha™ Direct 120 insulation. This fabric was originally developed for the U.S. Special Forces in order to provide them with an ‘advanced’ insulation piece in their uniforms, which all sounds very impressive. The aim behind the fabric is to provide a highly breathable material that will readily wick moisture through when you’re on the move but then when you stop, keep that moisture transfer going so that you don’t end up with a wet and cold layer; essentially meaning the fabric dries out really fast without you needing to shed a layer and expose your skin to the elements in the process. Polartec have labelled this as so-called ‘Active Insulation’ – this sounds particularly useful for the highly changeable Scottish weather. Indeed, Rab have used this fabric before on their Alpha Direct and Alpha Flux Jackets to great effect. The Alpha Flash is essentially these jackets with all the outer and inner layers removed, leaving only the Polartec Alpha Direct 120 insulation. Rab claim this is a radical reinvention of the traditional mid-layer, so we were very interested to see how it performed.

Simply put, the Alpha Flash is an excellent mid layer fleece. Over the past 4 months we've used the Alpha Flash winter climbing, ski touring and a week’s skiing in the French Alps, and even as a general fleece to keep warm down at the climbing wall. The Polartec fabric is wonderfully soft; it feels great on top of a baselayer and even directly next to the skin it is a delight to wear! We had a somewhat unintended test of this back in November when a rather smart reviewer forgot their baselayer for a winter route in the Cairngorms and had to wear the Alpha Flash as a baselayer. It performed brilliantly and kept us warm and sweat-free all day which was very impressive.

The fit is great – slim fitting which means there is little to no excess fabric when worn over a baselayer. The fleece features stretch panels on the underside of the arms and side of the fleece meaning that there is no restrictive movement whatsoever. Being so thin and light it barely feels like you’re wearing anything extra, which is great seeing as it is so warm when on the move.

At the end of the day it is just a fleece, so £100 seems quite steep, but for such an effective mid layer the clear benefits over a traditional fleece are probably worth the extra cost.

The only thing we didn’t like was the chest pocket which doesn’t quite fit a larger phone (5.3 “ screen) but this is very minor – it will fit most phones quite easily.

We look forward to using this fleece throughout the rest of the winter and in to the rock season – we expect it’d make an ideal layer climbing in the mountains where warmth and breathability are most needed.

Things we like: Excellent breathability, lightweight, very versatile mid layer.

Things we don’t like: Chest pocket a little too small, expensive for a fleece.

Succinct Gear Reviews are a collaborative team of reviewers based in Glasgow, Scotland. They have varied interests including; hill walking, climbing, mountaineering, camping, backpacking, kayaking, skiing, mountain biking and running which make them suited to reviewing a host of different outdoor products.