The Mythic Ultra 180 uses Rab's Tilt reflective lining . Photo: Bob Smith/grough

Price: £550
Weight: 429g including stuffsack
Packed size: 23cm x 17cm diameter
Fabric: outer and inner, 7 denier ripstop nylon
Insulation: hydrophobic goose down
Colour: black
Country of manufacture: UK

Rab’s Ultra sleeping bags are a new addition to its Mythic range and are designed and manufactured to offer good insulation at the lowest possible weight.

We tested the Mythic Ultra 180 which tips the scales at just under 400g without the stuffsack, and is designed to offer comfort down to 0C. There’s also a 360 version which offers comfort down to -7C and weighs 606g.

The 180 and 360 designations refer to the weight of 900-fill hydrophobic down in each model. The down is 90 per cent goose down/10 per cent goose feather with Nikwax fluorocarbon-free treatment to offer better performance in the damp. The down is RDS European certified and is contained in trapezoidal chambers which Rab says eliminates cold spots. The baffles are in a chevron design to better prevent the insulation migrating away from the centre of the bag during sleep.

The innovative aspect of the Ultra bags is evident when you look inside them. The lining material uses Rab’s thermo ionic lining technology, a process that involves incorporating titanium into the woven nylon to give it heat-reflecting properties. The Derbyshire company reckons this increases insulation for the user by about 30 per cent – worth up to 8C in extra warmth.

The sleeping bag packs up small. Photo: Bob Smith/grough

This enables Rab to use less down in its manufacture and a corresponding reduction in weight and bulk.

Another aspect of the Mythic Ultra 180 in line with its weight-saving design is the fact that it has only a one-eighth-length zip so if you get overwarm during the night, there is a limited ability to open up the bag for cooling. The zip, which has a little glow-in-the-dark tab, unfastens to about upper-arm level, to enable you to get in and out of the bag.

There’s a neck collar within the rear of the hood and the hood itself has a single drawcord with spring toggle to cinch it around the head.

The foot box is angled slightly. The Mythic Ultra 180 comes with a stuffsack plus a cotton storage bag. Packed size in the stuffsack was about 25cm x 16cm diameter so, combined with its low weight, makes it a good choice for fast movers in the outdoors, or trekkers on a multi-day trip who want to keep bulk and weight to a minimum without compromising on comfort.

Length from toe box to the top of the hood was about 190cm.

Despite the short zip, we found no difficulty getting into or out of the sleeping bag. The hood cinched in nicely around the face to provide a snug fit.

Our testing was necessarily confined to a nearby outdoor campsite early during coronavirus lockdown – our back garden. With overnight temperatures varying between about 3C and 5C, we found the Mythic Ultra 180 just about warm enough while sleeping in baselayers. The nicely lofting down provides an impressive amount of insulation for such a light and packable sleeping bag.

The hood cinches well around the head and face. Photo: Bob Smith/grough

The ability to cinch the hood well around the face, coupled with the fact that the neck baffle stops heat escaping, made for a snug feel to the upper section of the bag. Feet were not quite as warm.

The glow-in-the dark zip puller, which we thought a slight gimmicky addition, was actually quite useful in the tent at night, and stayed visible right through to the morning.

In a small tent on a very cool night, there’s always some build-up of moisture, but this presented no problem to the Rab bag’s hydrophobic down, which wasn’t compromised by the slight damp. Equally, the TILT lining allowed good breathability and there was no build-up of moisture inside the bag during our sleep.

The Rab Mythic Ultra 180 sleeping bag gained grough's 'best buy' rating. Photo: Bob Smith/grough

As a cold sleeper, I felt the Mythic Ultra 180 just on the limit of comfort at 3C ambient temperature, while wearing just baselayers. Taking care not to compress the loft against anything such as pack or tent sides definitely helps. It has a ‘Rab sleep limit’ of 0C, but we’d advise putting on extra clothing to get comfort at that temperature.

But for a pack so small and so light, the performance of the Rab sleeping bag was impressive.

For colder conditions, the Rab Mythic Ultra at 606g and priced at £700, offers comfort down to -2C.

The sleeping bag will accommodate a person up to 1.85m (6ft 3ins) tall.

Warmth 23/30
Comfort 25/30
Weight 19/20
Quality 8/10
Value for money 6/10
Total score: 81/100

• The sleeping bag was supplied to grough by Rab.