Marmot Astrum Jacket | Review - Outdoors Magic

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Marmot Astrum Jacket | Review

Marmot's medium-weight synthetic jacket uses and active fill and fabrics to up comfort on the move compared to more traditional puffy insulation.

‘One of the new generation of ‘active’ insulated jackets, the Astrum is decently warm but still comfortable on the move as long as you don’t burn too hot or move too fast’

Outdoors Magic: Soft, comfortable, stretchy and reasonably light. Fairly breathable and comfortable, adjustable, insulated hood, toasty fleece-lined pockets. Good wind resistance.

Outdoors Tragic: Cut is on the generous side for a medium. Not as breathable as Polartec Alpha.

Outdoors Grabbit? One of the new generation of active insulated jackets, the Astrum’s more breathable than traditional synthetic duvets, but not as effective as Polartec’s Alpha. For us, it had to be pretty cold before we were comfortable on the move, but if you run cooler, it may be more versatile for you. The cut is ‘athletic’ but actually quite generous for the nominal sizing, it feels nice and the features like the hood, pack-friendly pockets, hem and cuffs are all up to scratch.


Astrum Jacket Ratings

Outright Warmth 




Full Specification

Synthetic filled jacket / Thermal R Active stretch synthetic insulation / 90g body and top of sleeves/60g side panel and bottom of sleeves / stretch outer and stretch AirExchange lining fabrics / Attached Hood with Peripheral Cord Adjustment / Elastic Bound Cuffs / adjustable hem / pack-compatible pockets / Attached Hood with Peripheral Cord Adjustment / ‘athletic fit’

Full Review Below

The hood works nicely, it's insulated and can be adjusted front and rear to move with your head - Photo by Lukasz Warzecha
It will also fit over a climbing helmet if you want to use the jacket on more technical terrain - Photo by Lukasz Warzecha

Marmot Astrum Jacket – The Fill

Nestled inside the Astrum’s understated, slightly stretchy, olive-green shell is something called Thermal R Active. It’s a synthetic, but more importantly, it’s one a new generation of synthetic fabrics that have been designed to be non-migratory.

‘You can use more air-permeable/breathable materials, which in turn ups the overall breathability of the garment’

In simple terms, that means they don’t try to work their way out through the fibres of the fabric encasing them and that in turn means, you can use more air-permeable/breathable materials, which in turn ups the overall breathability of the garment and means it can be used more on the move without the familiar steamed pudding feel.

The fill also has characteristic damp-tolerant properties. Bear in mind that the ‘active’ bit is all relative. The fibres are quite a passive medium and our overall take is that it’s not as effective solution as Polartec’s pile-based Alpha insulation. Our testing bore that out.

Synthetic Sandwich

The jacket’s certainly more comfortable on the move than an old school traditional synthetic with the fill sandwiched between two layers of completely windproof fabric, but we found it had to be seriously cold for us not to overheat quite fast with any sort of serious pace on.

That’s all going to be relative both to your personal steam rating and the outside temperature and humidity, but we suspect it’s best suite to cold-blooded folk in cold, dry conditions. As ever, your mileage will almost certainly vary.

Twin hand-pockets sit just above pack-belt level if you're tall enough and have a luxurious micro-velour fleece lining - Photo by Lukasz Warzecha
The big plus of the hood adjustment options is that it moves properly with a bare head as well as with a helmet - Photo by Lukasz Warzecha

Marmot Astrum Jacket – Performance

The Astrum is part of a new generation of medium warm synthetic jackets which are also claimed to be breathable enough to use on the move. It started with Patagonia’s original Nano Air Hoody, which for us at least, tried a little too hard, with the result that its was barely wind resistant.

The principles are the same though. A fill that doesn’t migrate gives you the ability to utilise fabrics that aren’t totally wind and down-proof, which in turn means air can pass through them more easily.

In the Astrum’s case, the outer fabric is more or less windproof, but the liner is a much more open weave, which means heated, humid air can at least make its way into the insulation rather than being held close to the body.

American Athletic

The fit is described as ‘athletic’, but is quite generous in UK terms. We’d say our medium fell somewhere between a normal medium and a large, definitely not snug. It’s also longer than average. It has a nice, soft, comfortable feel to it and the detailing is good.

No problem with the luxurious fleece-lined hand-pockets, sigh… The adjustable hem, non-adjustable cuffs and the hood. The hood is a good one. It will take a helmet if you choose, but top and front adjusters mean it snugs down properly onto a bare head and moves with it. Nice.

Somewhere In The Midde

In terms of breathability, we’d say it falls somewhere between a traditional synthetic jacket and something like Polartec Alpha. We could wear it in cold conditions when we were moving relatively steadily, but hitting a steep up and working hard invariably overwhelmed it fast.

If you run cool, it should work better and may live up to Marmot’s ‘put it on in the morning and leave it on all day’ claim. If you run warm though, we suspect you’ll be taking it off on some of the ups unless it’s very cool.

A more air-permeable outer fabric might help, but then you’d lose out on some of the Astrum’s wind protection. Swings and roundabouts.


The jacket has a single inside zipped pocket on the righthand side. Unusually the zip gets a garage up top – Photo by Lukasz Warzecha

Marmot Astrum Jacket – Verdict

‘Active’ insulation is a bit of a buzz-word at the moment. As well as the Astrum, we have the single-minded Black Diamond First Light, the VauDe Bormio, the Rab Alpha Direct and Alpkit’s new Katabatic Jacket.

Marmot’s offering is nicely designed, generously cut and works well up to a point. It’s not a jacket we’d recommend if you run hot, but for steady use, by colder-blooded folk in winter conditions and for more static stuff it works reasonably well and has the traditional synthetic water-resistant virtues too.

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