The Mammut Sphere Alpine Spring is the lightest bag in our test at just 622g but it still manages a -1 deg C rating. It does feel light and soft and is very compressible with its high-quality down fill and a lightweight shell fabric making it very small in your rucksack. Some of the overall weight is cut from the features; for example the two-way zip is three-quarter-length with an internal baffle and an anti-snag channel made of webbing. There is no Velcro securing tab but there is a fabric zip ‘garage’ to keep the zip-pull in place. There is no shoulder baffle but the basic shaped hood cinches in to seal in the heat. The hood also has a small peak, which might give added protection from the elements while bivvying or deflect condensation drips away from your face in your tent. The shape overall is comfy, with reasonable room around the arms and enough space to move your knees. The foot box is roomy and shaped to allow your feet free movement. There are hanging loops, and the Mammut Sphere Alpine Spring comes with a storage sack and an excellent compression sack.
Weight (bag only) 622g
Size (length x shoulder width x foot width) 214x42x72cm
Packed size 17x24cm
Outer fabric Prolite TX
Inner fabric Light TX
Insulation 850+ European goose down
Construction wave box
Comfort temperature rating +4 deg C
Lower comfort limit -1 deg C
Extreme temperature rating -17 deg C
The Mammut Sphere Alpine Spring is a very light and comfortable bag that is warm for the weight of just 622g. The only drawback might be that temperature rating of -1 deg C, depending on the conditions you encounter.
Review by Peter Macfarlane
First published in Trail magazine June 2012