Quick verdict
Arc'teryx Thorium Hoody: 4.6/5
A 750-fill down jacket that stays sensible in the damp: Arc'teryx maps synthetic insulation into the shoulders and cuffs so the jacket keeps performing where pure down would fail. The warm layer for cold belays, cold summits and cold camp evenings.
- Active midlayer instead: Arc'teryx Atom Hoody (~£260)
- Down rival worth reading: Rab Microlight Alpine (~£240)
The full review is below.
The Arc'teryx Thorium Hoody is the down jacket in the Arc'teryx range, and it does a very specific job: it keeps you warm when you have stopped moving. Cold belays, cold summits, the hour after you pitch camp when the temperature falls off a cliff. It uses warm 750-fill-power goose down through the body and sleeves, so the warmth-to-weight is excellent, but the detail that makes it work in Britain is what Arc'teryx does with the damp-prone zones. This is not a waterproof, and it is not a jacket to sweat in on the climb. It is a warmth layer, and judged as one it is one of the most sensible down jackets you can buy for the UK hills.
This review is a spoke off our full Arc'teryx jackets explained hub, where the Thorium sits alongside the Beta shells and the Atom midlayers. If you are trying to work out where a down jacket fits in the wider range, start there. If you already know you want warmth at rest, read on.
The verdict up front
Buy the Thorium if you want proper, packable, stopping-warmth and you are prepared to keep it dry under a shell when the rain comes. The 750-fill down delivers a lot of heat for very little weight, and the synthetic-mapped shoulders and cuffs solve the one real weakness of down in a wet climate. It is expensive, and there are cheaper down jackets that keep you just as warm on a dry day. What you are paying for is the build, the fit and the intelligence of where the insulation goes.
Do not buy it as your do-everything midlayer. Down is the wrong choice for a layer you plan to work hard in, because trapped body moisture is exactly what flattens it. For an active, breathable, damp-tolerant layer you want the synthetic Atom instead, and our Atom vs Atom SL comparison covers that side of the range. The Thorium is about warmth at rest. Keep that distinction clear and the jacket makes complete sense.
Buy the Arc'teryx Thorium at Tiso
Who the Thorium is for
The Thorium suits the walker who already has a shell and a moving layer sorted, and now wants the warm jacket that lives in the top of the pack for when they stop. On a UK winter hill day that is the piece you pull on at the trig point while you eat, or at the belay while your partner leads, or in camp once the walking heat has drained out of you. It is warmth you carry and deploy, not warmth you march in.
It is also a strong choice for cold-but-dry conditions worn as an outer layer: a frosty morning start, a still, clear winter summit, a crag session where you are stationary between climbs. In those situations the down does its best work, lofting up and holding a big cushion of warm air for very little weight on your back.
Who should look elsewhere: anyone wanting one insulated jacket to hike in for hours in changeable weather. That is a synthetic-midlayer job, and the Atom does it better. And anyone expecting rain protection: the Thorium is not waterproof, and no amount of DWR on the face fabric changes that. It is a layer, not a shell.
The down, and Down Composite Mapping
The body and sleeves are filled with 750-fill-power goose down. Fill power is a measure of how much a given weight of down lofts, so a higher number means more warmth for less weight. At 750 the Thorium is warm and light without straying into the ultra-premium, ultra-fragile territory of the highest fill powers. It is a sensible, hard-wearing grade of down for a jacket that is going to get real use.
The clever part is what Arc'teryx does at the shoulders and cuffs. Those are the zones that get damp first: pack straps press and trap moisture across the shoulders, and cuffs soak up whatever your gloves and sleeves are carrying. Wet down collapses and stops insulating, which is the classic failure mode of a down jacket in a damp climate. So instead of running down all the way out to those areas, Arc'teryx maps synthetic CoreLoft insulation into them. Synthetic keeps lofting and keeps insulating even when it is damp, so the jacket carries on performing exactly where a pure-down design would be quietly failing.
Arc'teryx calls this Down Composite Mapping, and it is the single reason the Thorium makes more sense in Britain than a lot of pure-down rivals. It is not a gimmick. It targets the two spots on a down jacket most likely to wet out and reinforces them with the one material that does not care about moisture. For anyone hillwalking in a climate where damp is the default rather than the exception, that is exactly the right piece of engineering.
If you want to go deeper on down versus synthetic for UK conditions, and on the Rab down jackets that compete with the Thorium (the Microlight Alpine, Electron Pro and Nebitron Pro), our Rab insulated jackets guide is the piece to read next.
Fit, weight and packability
The Thorium follows the trim, athletic Arc'teryx cut, sized to layer cleanly over a baselayer and a light midlayer without turning you into a barrel. The hood is insulated and adjustable, cut to work over a beanie and to seal in warmth around the neck, which matters a great deal on a cold, still summit. The hem and cuffs close down well to stop warm air escaping, and the elasticated cuff sits comfortably under or over a glove.
As a down jacket it is light and it packs down small, stuffing into its own pocket or the top of a rucksack without eating your carrying capacity. That is the whole appeal of down: a lot of warmth that disappears into a small, light package when you are not wearing it. On a winter day pack it is the insurance layer you barely notice until the moment you need it, and then it earns its place instantly.
Layering-wise, treat it as the top warm layer. Baselayer, moving layer, shell for the rain, and the Thorium over the top when you stop. In truly foul weather you can wear it under a roomy hardshell to keep the down dry while it does its job, which is the standard way to run a down jacket in the British hills.
Buy the Arc'teryx Thorium at TisoPros and cons
- Excellent warmth-to-weight from 750-fill goose down
- Synthetic-mapped shoulders and cuffs keep it performing in the damp
- Packs small and light for the warmth it delivers
- Trim, well-cut Arc'teryx fit with a proper insulated hood
- The most sensible pure-warmth down jacket in the Arc'teryx range for UK use
- Expensive next to warm down rivals from Rab and others
- Not waterproof, and down needs keeping dry under a shell in rain
- Wrong tool for high-output moving; that is the Atom's job
- Warmth at rest rather than an all-day active layer
Best for
The walker who already owns a shell and a moving layer and wants a packable, properly warm down jacket for when they stop: cold belays, cold winter summits and cold camp evenings. If you want a layer to hike in rather than rest in, choose the synthetic Atom instead.
