These New Sleeping Bags Are Impossibly Light Thanks to an Innovative Ingredient

Mountain Equipment’s Xenith sleeping bags take a page from the award-winning Oreus Jacket’s playbook — one weighs less than a pound.

mountain equipment xenith extreme light sleeping bags macro

By Steve Mazzucchi

Published March 27, 2025

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One big upside of a brand making a variety of products in the same general space is cross-pollination.

In other words, the opportunity to leverage a breakthrough with one category toward other offerings, where it might be even more impactful.

That appears to be what’s happening with the latest release from Mountain Equipment.

mountain equipment xenith sleeping bag detail — RDS certified 900-fill goose down insulation ensures the new Xenith bags are exceptionally toasty.

Having made a big splash with its Oreus jacket last year, the UK-based alpinist brand has added one of its key elements to sleeping bags, helping them maximize warmth while minimizing weight.

Considering the lightest of the new Xenith Extreme Light Sleeping Bags tips the scales at well under a pound, that’s pretty compelling news.

Plasma power

The key tech Mountain Equipment is carrying over here is the outer fabric that made its debut in the Oreus, which not only won an ISPO award but also, more importantly, cracked the top 10 of last year’s GP100.

mountain equipment xenith sleeping bags lifestyle — Light and breathable Plasma 10D outer fabric help you move swiftly and stay protected at high elevation.

Said fabric is Plasma 10D, which is notably light and breathable, making it easier to not only carry these bags in your pack but also not overheat when night falls.

The fabric has also boasts a PFAS-free DWR treatment, adding a critical water repellent element to the mix.

mountain equipment xenith zipper detail — The bags employ tough zippers and multiple baffle designs to maximize warmth.

While the bags do not employ the other big Oreus innovation, Aetherm-augmented synthetic insulation, they do offer the potent natural properties of RDS certified 900-fill goose down.

Each bag also features a streamlined alpine fit and multiple baffle designs — including vertical box wall baffles in the chest and slant baffles in the main body — to boost thermal efficiency.

mountain equipment xenith drawcord detail — Available on the Xenith II and Xenith III, the cinchable anatomically shaped hood keeps your noggin toasty.

All three models are available in long versions, and each comes with a roll top stuff sack and a storage cube.

Top-notch trio

Here’s a quick look at the three options, which enable you to prioritize weight savings or warmth or split the difference.

At just 13 ounces, the Xenith I ($420) is the most streamlined bag, ideal for fast and light backpacking adventures.

Eschewing a hood to save weight, it has a stitch-through baffle back design, offset footbox and temperature rating of 5°C/41°F.

The Goldilocks-worthy choice, the Xenith II ($520) weighs 17 ounces and is rated 1C°/ 34°F.

It has a cinchable, anatomically shaped 5-baffle low-volume hood, a stitch-through baffle back design and a 3-baffle anatomically shaped offset footbox.

When warmth is paramount, the Xenith III ($680) is the best bet. Rated -7C°/19°F, it has more than twice the fill weight of the Xenith I and a weight of 24 ounces.

The hood is the same as the Xenith II’s, but the footbox has four baffles and the back boasts slant baffles to maximize warmth.