On paper the Marmot Phase has impressive stats, by using ultra-lightweight Quantum GL fabric and certified, responsibly sourced 850 Fill Power down it achieves a comfort rating of +6C and a comfort limit of -1C, this is at an overall weight of just 506grams or 539grams if you include the stuff sack.

So, by deducting the weight of the down from the total the shell of the bag comes in at just 266grams, this is mightily impressive and puts it among the lightest bags available for this level of performance. They even have the temerity to put a small zipped pocket inside the bag which just adds weight and is no use for anything really.

Performance wise I sleep cold so I normally plan based on the Comfort rating of the bag rather than the Comfort Limit, so, if I expect temperatures to drop to freezing I need a bag with a Comfort rating of freezing, which will probably have a Comfort Limit of -5C or thereabouts, and that’s assuming I’m sleeping in lightweight long-johns, a base-layer and socks.

The Marmot Phase 30 should therefore be good for me down to about 6 degrees. I experienced a range of temperatures in Iceland from a low of 8C down to a low of 1C, my impression is that the rating of the bag is perhaps a few degrees optimistic as I was a bit cold on my top half on the warmer nights, and had to wear additional clothing on the colder nights.

Although this is most definitely an ultralight sleeping bag it has some good features, a full length two way zip allows you to vent from the foot of the bag should you need to. The zip is claimed to have an anti-snag slider, but I’m not convinced, despite having this and an anti-snag strip alongside it I found it snagged a whole lot, but it was also easy to clear the snag – which might be the functionality referred to on the zip slider. I liked the luminous zip puller.

The cut of the bag is narrow but it didn’t feel cramped and I’m quite bulky, it achieves some of its weight saving by having a narrow leg section but opens out into a larger foot compartment, some people might find this type of cut restrictive but I didn’t and it’s no worse than other bags in this category. The hood design is excellent, it was easy to keep it snug round my face and like most quality sleeping bags it has a zoned construction to keep the down where it should be.

Details about the bags rating and construction appear as transfer labels on the inside and outside. The main one covers the EN test results, on my bag this deteriorated quickly and flaked off in tiny pieces, which was a bit annoying – it could be a one-off though because the other transfers have stayed in good condition.

In summary; It’s an excellent ultralight sleeping bag with a few niggles and possibly a slightly optimistic rating.