Wild CampingOEXSleeping Bag

OEX Leviathan EV 900 sleeping bag review: affordable winter warmth

Is this the best budget 4-season down bag on the market?

✓  RecommendedOEX Leviathan EV 900 Weight1,370 gComfort rating–9°C (stated)Price£170 The good✓  Very affordable at £170 (less on sale)
✓  Great warmth to weight
✓  Comes with stuff and storage sack
✓  Shoulder baffle locks in heat
✓  Hydrophobic duck down
✓  Soft, comfortable inner
✓  Durable water-resistant outer
✓  Zip protective strip — no snags
The not-so-good✗  Temperature ratings are optimistic
✗  Sheds feathers through the thin inner
✗  The colour is truly ugly
Check price at Go Outdoors →

At a glance

Overview

The OEX Leviathan EV 900 is a 4-season down-filled mummy sleeping bag sold by Go Outdoors, Blacks, Millets and Ultimate Outdoors. Designed and sold under the OEX banner — the most premium of the stores’ own brands — the Leviathan EV 900 has become a flagship product, with hundreds of fans all over YouTube. Head into the Lake District in mid-January and peek into the tents you spot — we would bet you would see the Leviathan’s unmistakable off-yellow hue emanating from at least a quarter of them.

The first thing to be aware of before you buy this bag is that it weighs a relatively heavy 1,370 g. For that, however, you get 900 gsm of 600-fill power duck down, making the bag lofty, comfortable and a joy to sleep in. It also comes with a huge shoulder baffle, a comfortable hood that can be cinched tight around your head, and a handy little pocket on the zip for small nick-nacks in the night.

The OEX Leviathan EV 900 also comes with a stuff sack and a storage bag that allows the bag to stay lofted when not in use for extended periods. It packs down to roughly the size of a standard football and lofts back up in no time (especially if you fluff it as you toss it into your tent). The ethically sourced down is also hydrophobic, meaning it will maintain some loft even when wet — pledging to keep you warmer than non-hydrophobic coated feathers, which is always ideal in the UK’s soggy climate. OEX list this bag as having a comfort temperature of –9°C, a lower limit of –16°C and an extreme rating of –39°C (tested per EN13537). Having used the bag for over three years, we have some thoughts on those numbers — which we cover below. When bought with a Go Outdoors Discount Card, it has an RRP of £170. On sale, it regularly drops to £120 or less.

What does fill power actually mean?

Fill power is a marker for understanding the quality of down versus the volume. It measures how much the down lofts back up after being compressed — higher-quality down lofts more. In general, the higher the fill power, the fewer feathers you need to achieve the same effect, making down products lighter, more packable and pricier. In the Rab Mythic 600 (£640), you get 600 g of 900-fill power goose down. In the Leviathan, you get 900 g of 600-fill power duck down — OEX had to use 150% more lower-quality duck down to achieve a similar temperature rating, making the Leviathan nearly 500 g heavier as a result. But then the Leviathan also costs less than a third of the price.

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How we tested

We have had this bag in our possession for over three years. We took it on freezing winter camps in Germany’s Black Forest National Park, used it on numerous summits throughout Bannau Brycheiniog and Eryri National Parks, slept in it on Dartmoor (including a super chilly deep winter camp where the mercury hit –13°C without wind chill), and even used it at the height of summer. After three years and countless nights, here is what we think.

Features and performance

Warmth: honest numbers

OEX claim that this bag can keep you comfortable down to –9°C when wearing nothing but baselayers. Having slept in it in temperatures approaching –9°C numerous times, we absolutely cannot support this claim. Though undeniably warm, for us the bag tops out at around –5 or –6°C in comfort. When we slept in it in –13°C, we had on baselayers, a jumper, a down jacket, thick socks, a hat and gloves — and even then, we were not baking. For UK use, however, we think the bag delivers enough warmth to reasonably be considered a true 4-season sleeping bag. We would be happy using it on practically any winter camping trip throughout the UK, and would only upgrade to something warmer for camping at serious elevation or in uncharacteristically harsh conditions.

Pack size, comfort and durability

Pack size-wise, the OEX Leviathan EV 900 is a reasonable size at this price point. Using the provided stuff sack you can get it down to the size of a watermelon or a standard football. To maximise malleability in your pack, we take to packing it in a dry bag — pressing out the air almost vacuum-packs it, leaving you with a mouldable pouch you can fit into any compartment.

One thing we have gotten used to is the inevitable plucking of feathers off our baselayers the morning after. This thing sheds like no other down bag we have used — presumably because the soft, thin inner (a joy to sleep in) allows duck feathers to penetrate when you roll around overnight. Initially we worried about losing insulation altogether, but after three years and over 50 nights in it, the bag has not lost any of its warmth or loft whatsoever.

The materials are soft, cosy and a joy to sleep in. The outer is durable and reasonably water-resistant — which we found out when we spilt 500 ml of cold water over the bag on a chilly winter’s night. The zip is also lined with a thick strip of protective material, which minimises snags and ensures you do not accidentally tear the soft inner while zipping up.

“After three years of abuse, would we buy another for £170? Absolutely. All we ask is that OEX consider a colour change.”

The looks

Despite the value for money, this is one thing we would love to talk to OEX about: what on earth is up with that colour? Have you ever seen a less appealing shade of yellow? Luckily, you only sleep in this thing, meaning your primary interactions will be in the dark. But the unusual yellow hue seems to have made this bag instantly recognisable — and easy to spot lurking in the back of many a YouTube video.

Our verdictThree years of abuse. Still going strong. Would we buy another? Absolutely.We really rate the OEX Leviathan EV 900. For the price, we think you would struggle to find anything even remotely comparable on the market right now, especially in terms of warmth. The reasonably small pack size and weight make it a solid all-rounder for numerous adventures. You can comfortably carry it for miles on winter hikes and extend its use to bikepacking or fastpacking trips if you have room in your setup. The temperature ratings are a touch optimistic — be honest with yourself about that — and the colour makes the bag look like it needs to see a doctor. But at £170, we would buy another in a heartbeat.Buy the OEX Leviathan EV 900 at Go Outdoors →

FAQs

What are the OEX Leviathan EV 900’s temperature ratings?Comfort: –9°C, Limit: –16°C, Extreme: –39°C (EN13537 tested). In our real-world experience, the bag tops out at around –5 or –6°C in comfort conditions — the stated ratings are somewhat optimistic.

How warm is the OEX Leviathan EV 900 in real-world conditions?Plenty warm well below zero. In our experience, we have comfortably slept in nothing but baselayers down to –5 or –6°C. Beyond that, we would recommend adding a liner or wearing a warm jacket inside.

Is the OEX Leviathan EV 900 easy to carry in a backpack?Yes. It packs down to roughly the size of a football and weighs just over 1.3 kg. Vacuum-sealing it in a dry bag lets you mould it into whatever shape fits your pack best.

Is the OEX Leviathan EV 900 worth the money?Yes. At £170 with a Go Outdoors Discount Card — and often as low as £120 on sale — it represents unbeatable value for a warm 4-season winter sleeping bag. After three years of abuse, we would buy another without hesitation.