Fill
Fill weight: 650 g (size M)
Fill power: 900 EU (970 US) white Polish Goose down
The most important part of a sleeping bag specification as the combination of fill weight and fill power (FP) is what provides the sleeping bag's ability to insulate.
550 g of 900 FP down will fill the same volume as 725 g of 800 FP down or 825 g of 700 FP down.
Construction
Baffles: Slant box wall on top and bottom
Hood: Adjustable cowl
Neck: Full adjustable baffle
Zip: Full length #5 YKK
Zip baffle: Double
The construction describes how the down is held in place (otherwise all the down would fall to the bottom) and what features are incorporated to maximise heat retention or, conversely, regulate your temperature. The Firelight 650 has sufficient down fill to warrant more sophisticated features such as a full-length side baffle, double zip baffles and an insulated neck baffle.
Fabrics
Shell: 29 g/m² 15 denier nylon (Pertex Quantum)
Lining: 29 g/m² 15 denier nylon (Pertex Quantum)
Lightweight fabrics allow the down to loft and reduce the weight of the bag. Although there are lighter-weight versions of the Pertex Quantum fabric we are using, they offer a negligible saving in overall weight and, having a lower tear strength, are easier to damage.
Bags:
Stuff sack: 25 g
Storage bag: 75 g