Force ten have used an incredible amount of fantastic technical features when designing this force ten altitude 750 down sleeping bag in order to achieve the maximum warmth to weight ratio with the lowest possible pack size available making this a fantastic sleeping bag for backpacking in 4 season conditions the altitude is a 650 fill power 9010 duck down sleeping bag with trapezoidal shaped baffles to reduce heat loss it also has a thermal embrace elasticised lining to increase trapped warm ai