It’s early morning and despite the fact that it’s mid-summer, it’s surprisingly cold outside. You know you’re going to warm up quickly because you’re heading out hiking, but you need a little more than just your lightweight baselayer to keep you warm for the first few kilometres. This is where the Arc’Teryx Atom SL Hoody comes in.

This is an impressively versatile top, designed to be worn as a midlayer in cold conditions or as an outer layer when needed. The insulation is ‘CoreLoft’, a material Arc’Teryx themselves developed which has crimped synthetic fibres of various sizes designed to trap air and retain warmth.

CoreLoft is not only impressively warm, it’s also lightweight, packs down small and dries quickly when wet. The Atom SL features a lightweight version of the insulation and only in critical areas (around the core) so the jacket can pack down small.

“It’s an impressively versatile top, designed to be worn as a midlayer in cold conditions or as an outer layer when needed.”

The shell of the Atom SL is highly breathable and treated with Arc’Teryx Nu water repellency. The StormHood is also DWR coated, making it rain-resistant, if not completely waterproof. The side panels under the arms are made of lightweight fleece for better ventilation, so you don’t build up too much of a sweat as you warm up.

Arc’Teryx have kept the fit of this relatively slim, which helps with breathability and means there’s no extraneous fabric to get in the way of carabiners, climbing ropes or any other gear you might be using.

The best thing about the Atom SL though is how lightweight and portable it is. Let’s face it, if you know the weather’s going to get hotter, the last thing you want to be lugging around is a big heavy jumper or jacket. The Atom SL weighs a mere 260g and packs down to the size of a grapefruit, making it the perfect thing to sling in your pack “just in case” – because in the British summer at least – you never know when the weather might turn.