Mountain Equipment Xenith III (373g)

The Mountain Equipment Xenith range of Extreme Light sleeping bags provide maximum warmth for minimal weight. With features and fit that ensure comfort night-after-night, with 900 fill-power Goose Down and the incredible Plasma 10D fabric, these bags are perfect for technical routes multiday routes in the Alps and Greater Ranges.

The Xenith III is a very warm and light bag for when every gram counts. Perfect for ultra-light backpacking and trekking in the high mountains during summer and at lower altitudes in Spring and Autumn, or for high alpine bivis. Supplied with roll-top stuff-sack and storage cube.

Fill: 373g of 90-10 900+ USA Fill power Goose Down.
Shell & Lining: Plasma™, 26g/m², 10D Nylon with fluorocarbon-free DWR.
Baffle Walls: Mesh Stripping, 15g/m², Nylon.
Zip: 140cm  two-way YKK® #5 Coil.
Construction: Ground Level Seams.
Baffle Type: Vertical Slant Baffles with Slanted Box-Wall Baffles.
Footpiece: 4 baffle Sharks Toe™.
Hood: Down Control 5 baffle with low volume.

Good Night's Sleep Guaranteed: -7ºC.
Comfort: -2ºC.
Comfort Limit: -8ºC.
Extreme: -26ºC.

ISO EN Sleeping Bag Temperature Ratings
ISO 23537 is the international standard for sleeping bags and requires a thermal manikin test which produces four temperature results - Upper Limit, Comfort, Limit (also written as Transition) and Extreme. There is no legal obligation to use this standard though most reputable brands do. There is an exemption for military sleeping bags and sleeping bags for extreme temperatures, ie a comfort range of below -25°C. 

Upper Limit: the highest temperature at which a standard man is able to have a comfortable night's sleep without excess sweating.
Comfort: the temperature at which a standard woman can expect to be comfortable in a relaxed position.
Limit (or Transition): the temperature at which a standard man can be not shivering in a curled position.
Extreme: the temperature at which a strong sensation of cold is to be expected and there is a risk of hypothermia.

For the purpose of these measurements, a "standard man" is assumed to be 25 years old, with a height of 1.73m (ie 5' 7", not very tall) and a weight of 73kg; a "standard woman" is assumed to be 25 years old, with a height of 1.60m (ie 5' 2.½") and a weight of 60kg.

It should be born in mind that the sleeping bag is just one part of the system and that other factors such as a good sleeping mat, how well fed you are and what clothes you are wearing, play a big part in how well you cope with cold temperatures. Plus, some people just feel the cold more than others - you'll know if you are one of them, and if so, plan accordingly.