Review: Mammut Crag IN Jacket

Coming in a disrespectful third behind fossil fuels and agriculture, garments and textiles produce about 10 percent of the annual global carbon footprint. While it’s easy to point fingers at fast fashion, the impact caused by the outdoor industry is not insignificant. However, there has been a collective push from within to find better, greener, and more sustainable ways to manufacture.

Serious outdoor brands are now making high-performance waterproof jackets without the use of PFAS “forever” chemicals, while initiatives such as NetPlus transform rescued fishing nets into usable materials, and the Single Use Plastics Project help to find new ways with plastic recycling.

PrimaLoft has been producing synthetic insulation, made from recycled plastic bottles, for years, but with Loopinsulation, Swiss climbing brand Mammut is taking sustainable warmth one step further by turning old climbing ropes into high-performance insulation.

The insulation manufacturing process used to create the Mammut Crag IN jacket starts with a mountain of industrial rope offcuts.

Photograph: Mammut

Developed in conjunction with Austrian firm Teufelberger—which has been making climbing ropes for Mammut since 2016—the closed-loop insulation manufacturing process used to create its first collection of insulated jackets, starts with a mountain of industrial rope offcuts. These randomly sized scraps of polyester would have previously been discarded, but now they’re untangled and sorted into individual strands. These strands are then brushed together and mixed with recycled plastic without the need for any binding chemicals. The result is a roll of highly insulating, completely recycled wadding.

The development of Loopinsulation started in 2018, when Mammut discovered that 13 percent of the company's CO₂ emissions came from rope manufacturing. So far the brand has recycled 12-tons of rope scraps, which doesn't seem like a lot, but the fact it has pushed the button and brought products to market should be applauded.

The outer fabric has a 20-denier thickness and is a comparable weight to other jackets at this price.

Photograph: Chris Haslam

Is rope recycling worth the effort though? I've been wearing the Mammut Crag IN Jacket ($179/£160) for the past few months and have been impressed by the windproof warmth of the thick polyester insulation. The internal wadding doesn’t have the same airy loft as a traditional goose down or synthetic loose-fill insulation such as Primaloft Gold, and it feels bulkier as a result. It's more like a quilted jacket rather than a performance outdoor puffer. But that's not to say it doesn't perform.

The combination of 100 percent recycled PFC-free DWR-coated polyamide outer shell and plenty of wadding (9.5-ounce / 270-gram fill weight) makes it a great choice as a daily cold weather jacket whether walking the dog, gardening, hiking local trails, or just hanging out. And with a respectable level of water resistance, and lack of natural fibers, there’s no danger of the insulation losing its warmth in the rain. The outer fabric has a 20-denier thickness, which is durable and a comparable weight (15.9 ounces/452 grams) to plenty of other jackets around this price point, but it certainly won't pack down as small due to the density of the insulation wadding.

Rope strands are brushed together and mixed with recycled plastic to create a roll of highly insulating, completely recycled wadding.

Photograph: Mammut

I was impressed with how easy the Crag IN jacket was to wash. Because the insulation is a sewn-in sheet rather than loose fill, it holds its shape easier and doesn't clump after a standard 30-degree-Celsius machine cycle. As such, I can imagine washing it more frequently than my traditional puffer jackets, although being polyester, there remains the annoying issue of microplastics in the water system.

When I asked Helena Theba, Material Management Lead at Mammut, she told me that the Loopinsulation insulation had “impressive technical properties that are directly comparable to industry standards like Primaloft Gold” but did also “recommend other insulation with higher loft for high-output alpine activities.” This is a fair point, one often overlooked by the general buyer who is arguably too quick to reach for the most technical outerwear regardless of whether it ever gets used as the makers intended.

Photograph: Mammut

For the 2024–25 season, Mammut has launched a couple of other options featuring Loopinsulation. These include the impressively versatile 2.5 layer Alto Light 3-in-1 HS Hooded Jacket ($369), which is both waterproof and insulating, while the Sender IN Hooded Jacket ($259) has 11.6-ounces (330-grams) of old rope insulation and a more versatile, climbing-specific stretchy shell made from recycled polyester and Spandex.

I've been wearing a battered old Patagonia Nano Puff ($239/£190) for years (alongside many other jackets that come through the test bench), and this too is made from 100-percent post-consumer recycled polyester. As someone who prefers to layer up rather than rely on one thick jacket, I don't think the Crag IN will become my go-to choice, mainly due to the boxy slightly stiff fit. But as a super-warm multipurpose jacket that's windproof, comfortable, and a brilliant example of closed-loop, open-minded recycling in action, it is hugely impressive.