Robens Serac 900 –20 °C sleeping bag review: serious warmth without the gimmicks
Built for cold wild camping nights across Britain, the Robens Serac 900 is a robust winter down bag that does exactly what it says on the tin — keeping you reliably warm below zero, without faff or fuss.
Robens Serac 900 sleeping bag
Ideal for: 4-season wildcamping, thru hiking, trekking
Not suitable for: Fastpacking, UL wildcamping
The Robens Serac 900 is a serious four-season sleeping bag designed for deep winter camps across the UK. With a –20 °C limit rating, 900g of hydrophobic duck down, and a sturdy yet packable design, it’s spot on for British hills and moors in freezing conditions. At £329 direct — and often much less if you shop around — it’s lighter and better value than many rivals, all while delivering dependable sub-zero warmth. If you’re after the best 4-season sleeping bag for the UK that balances weight, comfort, and price, the Serac 900 is a cracking choice.
The Good
Clean, easy design
Hydrophobic down
Great price for warmth
Very warm
Surprisingly packable
Excellent zip
The Bad
Heavier than more premium lines
Robens Serac 900 sleeping bag review
Robens are a well-regarded Danish outdoor brand known for producing solid, hardwearing kit that generally sits in the sweet spot between high-end performance and decent value. We’ve reviewed everything from their Elk River and Starlight 1 to the Chaser 1 — the tent we currently rate as the best ultralight three-season wild camping tent on the market. Time and again, we’ve come away impressed by Robens’ blend of sensibility and quality. They’re not a brand that indulges in flashy gimmicks. Instead, they seem to focus on gear that works well, lasts, and doesn’t overcomplicate things.
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The Serac 900 is Robens’ take on a classic four-season down bag. It’s aimed squarely at folk heading out into cold, damp British winters where snow, frost, and condensation are all on the cards. It tips the scales at 1.5 kg, which — for a bag with this much loft and warmth — is both confidence-inspiring and pretty reasonable for backpacking. It packs down to 34 × 25 cm, meaning it’ll slide into most winter packs without hogging space. Retailing at £329 direct from Robens (though often found for much less — sometimes close to half price at outdoor retailers like Outdoor Action), it undercuts a lot of similar-spec bags while still promising serious cold-weather chops.
How it stacks up against the competition
When lined up alongside other four-season down bags, the Serac 900 holds its own. The Therm-a-Rest Parsec 0°F (–18 °C) we reviewed previously weighs 1.28 kg and packs down a touch smaller, but comes in north of £400. The Mountain Equipment Helium 800 sits closer in weight at 1.39 kg with a –12 °C comfort limit, typically retailing around £380–£400. Meanwhile, the Rab Ascent 900 — another winter-ready option — weighs 1.55 kg with similar pack size but usually breaks £400 too. Factor in that the Serac 900 can often be found discounted well below its £329 RRP, and it starts to look like an even sharper deal.
Putting the Robens Serac 900 to the test
We’ve had the Serac 900 out on multiple wild camping trips through the British winter, where it’s faced everything from sleet to still, frozen mornings that turned our breath to ice. It’s seen frost-nipped bivvies on Dartmoor, where we woke to find our gear rimed in white, and snowy nights in the Brecon Beacons that demanded every bit of insulation we’d brought.
On one particularly frigid outing paired with the Robens Elk River One, we pitched up on a windswept shoulder just below the ridgeline. The temperature plunged overnight — so much so that when we cracked open the fly in the morning, the whole outside was crusted in frost. Inside the Serac 900, though, we’d been so snug we only realised how cold it really was once we stepped outside to brew up.
It’s not just the bitter nights that have impressed us. Even on damp, clammy winter camps — where condensation inevitably finds its way inside — the hydrophobic down did its job, refusing to collapse or clump. While we’ve not pushed this bag to its extreme –20 °C technical rating, we’ve tested it in every realistic scenario the British winter could throw at us. Each time, it’s kept us warm, comfortable, and crucially, confident enough to keep pitching up for more. It’s the sort of kit that lets you look at a frosty forecast and think, “yeah, let’s still go.”
A closer look at the features
The Serac 900 is refreshingly free of nonsense. It’s a classic mummy bag, shaped to trap warmth close while avoiding dead air that your body would otherwise waste energy heating. The snug hood pulls in tight around your face on bitter nights, blocking draughts without feeling claustrophobic. The footbox gives your feet enough room to move naturally — a small but crucial detail that stops you waking up cold from compressed insulation.
That EN13537 –20 °C lower limit rating is no marketing fluff. It’s a survival figure, sure — but it shows this bag is engineered for real winter use. In practice, it’s more than capable for any normal sub-zero British camp.
Then there’s the fill: 900g of 85/15 RDS-certified duck down, roughly 600 fill power, responsibly sourced and treated to resist damp. That hydrophobic treatment is key — on damp Dartmoor nights when condensation crept inside, it didn’t collapse or clump. It won’t perform miracles (no down does), but it gives you crucial leeway.
The recycled 20D 400T ripstop nylon shell hits a sweet spot of soft but durable. We’ve slept in it direct on the groundsheet, stuffed it in and out of its sack dozens of times, and it still looks new. The pack size of 34 × 25 cm is spot on for a proper winter bag, leaving you room in your pack for layers, stove and food.
Other touches we rate? That smooth, snag-free YKK zip that doesn’t jam when you’re half-asleep fumbling for a midnight wee. The well-baffled zip line and collar that seal in heat so you’re not woken by tiny draughts. And of course, its Out and About 2024 award simply underlines what we’ve found ourselves: it’s a smart, reliable, well-executed piece of kit. No surprise Robens aren’t changing much for next season beyond a new colour — the fundamentals are already nailed.
How the Serace 900 performs in the UK
The Serac 900 is right at home in the UK’s often unpredictable, damp and freezing winter conditions. It’s genuinely warm enough for typical British sub-zero nights — we’ve stayed perfectly snug on frost-covered Dartmoor bivvies and through snowy evenings in the Brecon Beacons without a hint of chill. Despite packing serious insulation, it compresses down nicely to 34 × 25 cm, so it slips into a winter rucksack without hogging all the space. At 1.5 kg, it’s no ultralight, but that’s a fair trade-off for dependable four-season warmth. The hydrophobic down handles our famously damp climate well, shrugging off condensation that would flatten lesser bags. All in, it’s the kind of sleeping bag that gives you the confidence to keep planning cold-weather wild camping trips across the UK, knowing you’ll stay warm, comfortable and properly rested.
Robens Serac 900 sleeping bag FAQs
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We’ve used it on nights well below zero in places like Dartmoor and the Brecon Beacons and stayed perfectly warm. While we’ve not pushed it to –20 °C, it’s proven itself as a safe, snug option for typical British winter temperatures.
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For a four-season down bag, yes. It weighs 1.5 kg and packs down to 34 × 25 cm. That’s smaller and lighter than many rivals in this warmth bracket, making it perfectly reasonable for wild camping without dominating your pack.
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Absolutely. At £329 direct from Robens — and frequently available for much less from outdoor retailers (sometimes nearly half price) — it’s not a budget buy, but compared to other genuine winter-ready down bags, it’s outstanding value. It’s a proper investment that delivers the warmth, comfort, and reliability you need for cold adventures in the UK.
Robens Serac 900 sleeping bag: our verdict
This is a genuinely excellent sleeping bag. It’s built for people who want to keep exploring Britain’s hills and valleys through the depths of winter, without gambling on warmth or faffing about with gear that tries to be too clever. You’ll pay more than for a generic bag off Amazon, sure — but for £329 direct (often much cheaper if you shop around — we’ve seen it close to half price at places like Outdoor Action), the Serac 900 is a proper, proven bit of kit that you’ll pull out every winter for years to come. If you’re after the best 4-season sleeping bag for the UK that balances price, performance and trustworthiness, it’s hard to beat.
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