*Previously branded as Forclaz

If you're after a lightweight down sleeping bag that doesn’t break the bank, the Simond MT900 5°C is an absolute gem. With a pack size that rivals premium options and a warmth rating that holds its own in British spring and autumn, it’s a solid pick for wild camping and fastpacking alike.

Simond MT900 5°C down sleeping bag

Ideal for: 3-season backpacking, wildcamping, thru hiking, fastpacking and bikepacking

Not suitable for: 4-season use

At just 830 grams and packing down to the size of a melon, the Simond MT900 5°C sleeping bag offers a very competitive spec for its price. Filled with 700 FP down and priced at £149.99, it balances warmth, weight and cost well. We’ve used it on bivy nights by the Thames and spring wild camps on Dartmoor, and it’s held its own. The roll-top compression sack is a thoughtful addition, and the hood’s better than expected. All things considered, it’s one of the better value down bags we’ve come across at this price point.

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Simond MT900 5°c down sleeping bag review

Simond is Decathlon’s high-mountain gear brand – and while it's not as widely known in the UK as Rab or Mountain Equipment, it’s been producing solid, budget-friendly mountaineering gear from its base in Chamonix since 1860. Yep, that long. While historically better known for hardware like ice axes and crampons, Decathlon has recently folded its trekking-focused Forclaz range into the Simond line, creating an even broader offering for outdoor types on a budget.

The Simond MT900 5°C down sleeping bag, the focus of today’s review, is part of that expanded range. It’s a lightweight, three-season down sleeping bag designed for trekking, bikepacking and wild camping in conditions from spring through to autumn. With a comfort rating of 5°C, a total weight of 830g (in size large) and a packed size that fits neatly in a fastpack or small rucksack, it’s clearly targeting fast-and-light adventurers who don’t want to splash out on top-tier gear.

It currently retails at £149.99 – and at that price, it’s seriously undercutting premium brands while delivering specs that easily hold their own. For comparison, Rab’s Alpine 200 is a popular choice among lightweight purists, coming in at 630g and boasting a minimalist design, but it retails for nearly double the cost (£270) and uses a lower-grade 650 FP down. While it’s undeniably lighter, we’d argue that the real-world warmth difference is negligible for most users, and the overall user experience is equivalent for half the price. At the other end of the spectrum, the OEX Chimera EV 500 is £30 cheaper at £119 (with a Go Outdoors membership), but the compromises are obvious. It’s over a kilo in weight, doesn’t pack down nearly as well, and uses a lower-quality 600 FP fill. It gets the job done for milder temperatures, but when you’re counting grams and litres, the Simond is clearly worth the extra spend.

There are of course even cheaper bags on the market, but they often rely on synthetic insulation, have large pack sizes, or miss the mark on comfort and build quality. With the MT900, you’re getting 700 FP down, clever baffle design, and a compression sack that genuinely compresses – all of which are rare at this end of the market.

All in, the Simond MT900 strikes an incredibly compelling balance of warmth, weight and price – and makes a strong argument as one of the best-value ultralight bags on the UK market right now. It’s a great example of how thoughtful design and smart material choices can deliver serious performance without an eye-watering price tag.

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Our experience with the Simond MT900 after a year of use

We’ve spent over a year sleeping in the MT900. In that time, it’s been out with us on a dozen nights across the UK – including a blustery wild camp on Dartmoor’s Great Mis Tor in spring, where temperatures dropped right to the comfort limit, a balmy summer filming trip in the Brecon Beacons, and a fastpacking adventure along the Thames in early autumn, tucked into the bottom of an Ultimate Direction Fastpack 30. Each time, we paired it with a good-quality mat (such as the Big Agnes Zoom UL), and occasionally added layers depending on the chill.

What we found, each time, was a bag that managed to walk the fine line between bulk and warmth remarkably well. While it took some getting used to the snug cut at first, we soon found our rhythm. As long as we respected the temperature guidelines and used the right mat, we stayed warm and comfortable. Even in the exposed terrain of Dartmoor, with wind slicing through the air outside the tent, we were cosy enough inside the MT900 to drift off with ease.

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Standout features of the MT900

The Simond MT900 doesn’t try to dazzle with overengineered gimmicks or premium-tier marketing speak – instead, it delivers a solid package of thoughtful features that actually matter to the people using it. From the quality of the down to the design of the baffles and the bag’s excellent compression system, everything here has been put together with care and a clear focus on performance-to-price value.

Take the insulation, for instance. The MT900 contains 90% grey duck feather and 10% grey duck down, rated at 700 CUIN. It’s not the absolute top-end fill you'll find in something from Rab or Cumulus, but for a sub-£150 bag, this is excellent stuff. The 700 fill power gives it strong loft and good compressibility, bouncing back nicely after being packed away.

Warmth and packability

Warmth-wise, the MT900 delivers what it promises. When used with a properly rated mat (we recommend an R-value of 4 or higher) and some decent layers, it provides reliable comfort right down to its 5°C rating. We’ve slept soundly in it during early spring and late autumn in the UK – and while colder nights will need a little layering help, that’s true of any bag in this weight class.

One of the real highlights is its packability, with the included stuff sack being a solid standout. Using a dry-bag-style roll-top closure, it allows you to squeeze the air out and reduce the pack size to something roughly melon-sized – ideal for fast-and-light setups where space is at a premium. The addition of a handle on the bottom is a small but incredibly useful touch, making it far easier to yank from the depths of a jammed rucksack.

The shape of the bag, described as "sarcophagus style," sounds a bit ominous but works well in practice. It's body-hugging for efficient warmth, but not claustrophobic unless you’re particularly broad or restless at night. The hood deserves a nod here too – it’s soft and cocooning without feeling restrictive. Fully done up, it makes a noticeable difference to overall warmth and adds a touch of luxury to chilly nights.

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Extra features

Zips are another common weak spot on more affordable bags, but we had few complaints here. The zip on the MT900 runs smoothly with minimal snagging, and the addition of decent baffles along its length helps keep draughts out. It did catch once or twice when rushed one-handed, but never to the point of frustration.

Inside the bag, there is a small internal pocket, but it feels more like a tick-box addition than a genuinely useful feature. It’s just about big enough for a phone or head torch, but we rarely used it – and to be honest, we’d happily trade it for a few grams of weight savings.

Additionally, the cleverly-designed baffle layout is worth a mention. Horizontal baffles wrap the upper body for even warmth distribution, while vertical ones around the legs and feet help keep insulation in place where it tends to shift most. It’s a simple but effective design choice that improves overall warmth without overcomplicating things.

Rounding things out, you get two hanging loops for drying and a breathable mesh storage sack for stashing the bag between trips. Nothing fancy here, but both do the job well and round off a very complete package.

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Simond MT900 sleeping bag FAQs

The Simond MT900 has a comfort temperature rating of 5°C, a limit temperature of 0°C, and an extreme rating of -15°C. The comfort temperature is where most users will sleep comfortably without extra layers, though individual preferences and conditions always play a role.
In our tests, the MT900 held its own down to 5°C when used with a decent sleeping pad (R-value 4 or more) and a few light layers. It's warm enough for typical UK conditions from spring to early autumn, though you’ll want to add insulation below that threshold.
Yes – very. At 830 grams and with a pack size about the size of a melon, it’s one of the most portable bags we’ve tested in this category (and at this price point). The roll-top compression sack is excellent and makes it a perfect fit for ultralight backpacking, bikepacking or fastpacking trips.
Absolutely. For £149.99, you get 700 FP down, smart baffle design, great packability and solid warmth. It competes with bags almost double the price and outperforms most of the budget competition. It’s easily one of the best-value down sleeping bags on the UK market right now — if not the standout winner!

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Our verdict after a year of UK use

Over a year of testing in a range of real-world British conditions, we’ve grown to seriously rate the Simond MT900. It’s warm, packs impressively small, and doesn’t weigh you down. Most importantly, it delivers all of that at a price point that feels almost too good to be true. Sure, it’s not the lightest bag out there. And no, the down quality isn’t best-in-class. But when you consider the combination of 700 FP fill, great warmth retention, clever baffle design and a compression sack that actually does its job – all for £149.99 – it’s a standout performer.

This is a bag that’s genuinely well-suited to UK three-season use. For wild campers, thru-hikers, fastpackers and backpackers operating on a budget – but who still want gear that delivers – the Simond MT900 is a proper no-brainer. We’ve tested bags that cost twice as much and left us colder, bags that weighed less but came with fiddly stuff sacks, and bags that promised compressibility but puffed back out the moment you turned your back. The Simond MT900 does none of that. It just works. And for that, we are confident in recommending it.