Insulation
There are two types of insulation: This is best for light weight and low bulk. Most down is now treated with a water-resistant coating to maintain loft and prevent clumping when wet. Most manufacturers use down that meets the Responsible Down Standard for animal welfare.
Synthetic: A good option for prolonged damp conditions, lower budgets or where weight is less important. For the same warmth rating, synthetic-filled bags will be heavier and less compressible than down-filled bags but they're durable, easier to wash and warmer when wet. There are high-end and budget bags.
Quilts
Because down insulation doesn't trap air well when compressed (i.e. when you're lying on it), quilts do away with the bottom side of the bag, but retain a footbox which generally extends to mid-calf. Provided a mattress is used, a quilt can offer similar warmth to a sleeping bag but with reduced weight and pack size.
Temperature rating
Ratings are approximate, however, most sleeping bags are now tested to the temperature ratings standard EN13537 or ISO 23537-1. These ratings help users compare and choose the right bag for the conditions they expect to use it.
There are three temperature ratings (though
