Rab Mythic 600 Sleeping Bag Review

Rab Mythic 600 Sleeping Bag Review: When Premium Down Actually Delivers

Lying in my Rab Mythic 600 sleeping bag on a bitter December night in the Langdales with temperatures plunging to -10°C and wind chill making it feel even worse, I was genuinely amazed to find myself almost too warm. I actually had to partially unzip the bag to vent some heat—a problem I’d never experienced with any previous sleeping bag. After two seasons of putting this ultralight down bag through its paces across British mountains, from summer wild camps in the Brecon Beacons to winter expeditions in the Lake District, I can honestly say it’s transformed my approach to mountain sleeping systems, though the premium price still makes my Yorkshire wallet wince.

This review comes from someone who’s discovered that sometimes expensive gear really is worth every penny, even if it hurts to admit it.

Why I Finally Invested in an Expensive Down Bag

The Budget Sleeping Bag Evolution

I’d been using the Alpkit Pipedream 600 for about two years, which at £200 was a significant investment for me at the time. It was genuinely good—600g of quality duck down, decent construction with a comfort rating around 1°C, and honest temperature performance. For most people, it would probably be perfectly adequate for British mountain conditions.

But here’s the thing: I’m naturally a cold sleeper. Even with the Pipedream 600’s claimed comfort rating, I’d often find myself adding layers or waking up chilly during shoulder season conditions. It wasn’t that the bag was bad—it just wasn’t quite enough for someone who runs cold. I’d end up wearing my Rab Geon Pull-On fleece inside the bag more often than I’d have liked, which rather defeated the point of having a lightweight system.

My usual approach was pragmatic: visit Go Outdoors or similar retailers, find something with a decent temperature rating that didn’t cost more than a weekend’s wages, and accept that wild camping meant being a bit uncomfortable. Over the years, I’d probably gone through six or seven bags, each following the same disappointing trajectory from adequate to useless.

The Breaking Point

The expensive lesson came during a spring photography trip to Snowdonia. I was carrying my Canon 5D Mark IV and lenses in my Lowepro PhotoSport Backpack PRO 70L AW III, trying to keep pack weight reasonable for the long approach to my planned wild camping spot near Snowdon. My bulky synthetic bag was taking up nearly half my pack space and weighing close to 2kg—space and weight I desperately needed for camera equipment.

When I finally crawled into it that night, despite the claimed 0°C rating, I was genuinely cold. I ended up wearing my Rab Geon Pull-On fleece and even my Rab Mythic Ultra Down Jacket just to get through the night. I spent most of the darkness calculating how much lighter and warmer a proper down bag would be, and wondering why I’d been so stubborn about spending money on something so fundamental to outdoor comfort.

The Research and Purchase Decision

Here’s where the story gets interesting, because this wasn’t a planned purchase at all—it was a series of coincidences that aligned perfectly to make an expensive bag suddenly affordable.

I’d been using an Alpkit Pipedream 600 for about two years, which I’d bought for £200 and was perfectly happy with. It did the job adequately, though it was heavier and bulkier than I’d have liked. Then three things happened almost simultaneously that changed everything.

First, I spotted the Rab Mythic 600 on sale at LD Mountain Centre for £462 instead of the usual £600—a significant discount that made it suddenly tempting rather than completely unaffordable. Second, I’d seen Andrew Beevers, a local wild camping legend, using the same bag during a chance encounter on a Lake District fell, and his enthusiasm for it was genuinely infectious. Third, I noticed that Alpkit had increased the Pipedream 600’s retail price to £300, making my two-year-old bag worth more secondhand than I’d expected.

Being a proper Yorkshire lad, I couldn’t resist doing the maths: if I could sell my Pipedream 600 for a decent price, the Mythic would cost significantly less than its intimidating retail price. I listed it on Facebook Marketplace for £185 and it sold within two days—meaning I’d only lost £15 on a bag I’d used extensively for two years.

Suddenly, a £600 sleeping bag was costing me just £277 (£462 minus £185 from the sale). The discount, plus getting most of my money back on the Alpkit, transformed an expensive purchase into something I could justify. Sometimes the stars align perfectly for gear upgrades.

What I Absolutely Love About This Sleeping Bag

Incredible Warmth-to-Weight Ratio: At just 925g total weight, this bag provides warmth that my previous 2kg synthetic bags couldn’t match. The 600g of 900 fill-power down creates an insulation system that’s genuinely impressive in its efficiency.

Outstanding Packability: The compression is remarkable—it stuffs down to roughly the size of a small watermelon. This has transformed my packing, freeing up space in my pack for camera equipment or additional layers.

Chevron Baffle Design Excellence: The baffle construction eliminates cold spots completely. The down stays positioned over your core where it’s most needed, rather than migrating to less useful areas.

Thoughtful Construction Details: The neck baffle forms a perfect seal against drafts, the YKK zip runs smoothly even when operated in darkness with cold hands, and the trapezoid boxwall construction maximizes thermal efficiency.

Hydrophobic Down Treatment: The Nikwax treatment means the down performs well even in typical British damp conditions. Unlike untreated down that becomes useless when wet, this maintains loft and insulation properties.

Hand-Filled Quality: Made in the UK and hand-filled, the down has never been compressed before first use, maintaining maximum loft and warmth potential from day one.

What Could Be Better Rab Mythic 600

Premium Price Shock: At £600, it’s genuinely expensive. The performance justifies the cost, but it’s still a significant investment that requires serious financial commitment.

Hood Adjustment Issues: The cinch system can be fiddly to adjust in darkness. When you’re cold and trying to seal out drafts, the system isn’t as intuitive as it could be.

Extreme Tapered Cut: The narrow profile maximizes thermal efficiency but can feel restrictive. If you’re used to roomier bags, the confined space takes adjustment.

Down Care Requirements: Unlike synthetic bags that you can stuff carelessly and wash roughly, this requires proper storage and careful maintenance to preserve the down’s loft and performance.

Real-World Performance Analysis

Extreme Cold Weather Testing

The bag’s performance in genuine cold conditions has been consistently impressive. During that memorable December night in the Langdales with temperatures hitting -10°C, I was not just warm—I was actually too warm. Having to partially unzip a sleeping bag in sub-zero conditions was a new experience for someone used to shivering in budget bags.

On the coldest Lake District winter nights, I sleep wearing my Rab Argon Pants and Rab Mythic Ultra Down Jacket inside the bag, creating a sleep system that’s genuinely bombproof against anything British winter can throw at it. This combination transforms the Mythic 600 from excellent to absolutely impenetrable warmth. The down’s loft creates an insulation barrier that feels almost magical compared to compressed synthetic fill from my previous bags.

Wild Camping Integration

For wild camping with my MSR Access 2 tent setup, the bag performs brilliantly. The compact packed size means it doesn’t dominate my pack space, leaving room for other essentials. During multi-day trips, the weight savings become increasingly apparent.

There’s genuine pleasure in the evening ritual of setting up camp with proper kit. Getting the MSR Access 2 pitched efficiently, firing up my Jetboil Flash for a hot brew, using my Flex Tail Gear Pump X to inflate my Therm-a-Rest NeoAir XTherm sleeping mat, then unpacking the Mythic 600 and watching it loft up into a proper sleeping system. It transforms the whole wild camping experience from survival into genuine comfort.

The bag pairs perfectly with my sleeping mat, creating a sleep system that handles British mountain conditions with confidence. The combination has kept me comfortable in temperatures well below what I’d previously attempted with the Alpkit Pipedream 600.

Durability and Longevity

After two seasons of regular use, including being stuffed into my Karrimor SF Sabre 75 expedition pack countless times, the bag shows no signs of down migration or loss of loft. The construction quality is evident in how well it’s maintained its performance characteristics.

The baffle system has proven robust—no weak points or areas where down has shifted permanently. The YKK zip continues operating smoothly despite regular use in various conditions, and the fabric shows minimal wear despite extended use.

Photography Trip Performance

For wild camping expeditions where pack weight matters significantly, this bag has been transformational. The quick setup and immediate warmth mean I can focus on enjoying the outdoors rather than struggling with inadequate sleep kit. During those perfect evening moments, knowing I can return to proper warmth makes the entire experience much more enjoyable.

How It Integrates With My Complete Kit

The Rab Mythic 600 has become the cornerstone of my four-season camping system. Combined with my Rab layering system—Cinder Downpour shell, Geon Pull-On fleece, and base layers—it creates a comprehensive approach to mountain comfort.

For extreme conditions, I can layer my Rab Mythic Ultra Down Jacket and Rab Argon Pants inside the bag, effectively creating a sleep system that handles anything British winters can produce. This layering approach transforms the system from excellent to bombproof.

The bag’s compact size integrates perfectly with my photography-focused packing strategy. In my Lowepro PhotoSport Backpack PRO 70L AW III, it occupies minimal space whilst providing maximum performance benefit.

Alternative Options

Mountain Equipment Glacier 700 (£520): A premium alternative offering slightly more insulation with 700g of down fill. The extra warmth comes with additional weight and bulk, making it better for static camping but less ideal for active mountain use. Features include similar baffle construction and hydrophobic down treatment. The fit tends to be more generous than the Rab, which some users prefer. At a higher price point, it represents the ultimate in cold weather sleeping bags but may be overkill for most British conditions.

Western Mountaineering Alpinlite (£480): This American-made bag offers exceptional build quality with 850 fill-power down and proven durability. The construction is slightly different, with sewn-through baffles that reduce weight but create minor cold spots. At a similar price point to the Rab, it offers different trade-offs—lighter weight but potentially less warmth in extreme conditions. The fit runs longer and narrower than European bags.

Rab Neutrino Pro 600 (£380): A more affordable option from the same manufacturer, offering similar down fill but with simpler construction. The baffle system isn’t as sophisticated as the Mythic, and the materials are less premium, but it still provides excellent performance at a lower price point. Weight is slightly higher at around 1.1kg, and packed size is larger, but it represents good value for those prioritizing cost over ultimate performance. For comparison, it’s lighter and warmer than the Alpkit Pipedream 600 but without the premium features of the Mythic.

The Honest Verdict

This sleeping bag represents everything I thought I didn’t need until I actually used it. The performance difference over budget alternatives is so significant that it’s transformed my approach to wild camping and mountain adventures.

Would I buy it again? Absolutely, without hesitation. Despite the eye-watering price, it’s proven its worth repeatedly through consistent performance in conditions where failure isn’t an option.

The reality: Sometimes expensive gear really is better, and this sleeping bag is a perfect example. The warmth, weight savings, and build quality justify every penny of the premium price.

Bottom line: Outstanding sleeping bag that delivers exactly what serious mountain users need. It’s staying permanently in my kit as the foundation of my sleep system, and I can’t imagine going back to budget alternatives.

Long-term verdict: After extensive testing, it’s become so essential to my outdoor adventures that I consider it one of the best investments I’ve made. For serious wild camping and mountain photography, the performance benefits far outweigh the initial cost shock.

The Rab Mythic 600 proves that sometimes the expensive option really is worth it, even if it pains a Yorkshire wallet to admit it. Excellent gear that transforms what’s possible in British mountain conditions.

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