The force 10 nano 0 sleeping bag has an incredibly small pack size and comes in at under a kilo making it a superb choice of lightweight 2 3 season sleeping bag force 10 have used the latest hollow fibre synthetic insulation 4t which achieves an improved warmth to weight ratio by trapping air in its patented channel structure they have combined a double layer construction with a specific layer of different weightsthichness of 4t insulation function to achieve greater insulation properties while