Nick B

Sleeping bags vary in weight depending on what type of conidtions you will be using them in.

If you're a serious camper, enduring long distance treks or expeditions then it's worth spending the extra cash on a 'down' filled lightweight sleeping bag.

Feather Weight

Down is a gift from nature, it's the thermal insulation which is grown by birds, and considering the harsh environments birds survive in, down is perfect full for a sleeping bag which will be used in similar cold conditions.

Sleeping bags filled with down outperform synthetic sleeping bags at a given temperature rating, down bags will be lighter and you can compress them into a smaller size when you pack them away.

This really important when you're treking as you want to carry a sleeping bag which is lightweight as possible, you also need something which will pack away really tight and small so as to not get in your way, down fills both these requirements.

Obviously, you will need  to choose a season class. You should always take into consideration your own tolerance to cold, i.e. if you have any underlying health conditions etc. Down can have its downsides though, when wet it does not dry as quickly as synthetic sleeping bags, but overall, if you're in a decent quality tent set up correctly you should not be worrying too much about the elements soaking your sleeping bag.

The quality of down is rated by cubic inches or 'cuin'. Basically the quality of the down relates to the thermal rating. The down is used for the insulation and the the support feathers offer the loft which helps to retain the heat. These two aspects of down fill are represented by ratio, usually the down is the higher percentage and the higher density of down will relate to a higher level of insulation.

Synthetic sleeping bags can also be lightweight but they do not offer the same insulation, if you're looking for a good quality warm sleeping bag which is lightweight then down is the way to go.