The number one function of your sleeping bag is to keep you warm at night. Beyond warmth, additional considerations include weight, shape style, fit and fill.

Key considerations.

1. Type of activity - single vs. multi-season use; temperature; likelihood of rain; type of camping (car vs. backpack vs. kayak); amount of use.
2. Features/fit - size (extra long, woman's size); shape (mummy vs. semi-rectangular vs. rectangular); fit; weight; compressibility; price.

The biggest decision in choosing a sleeping bag is whether to have down or synthetic fill.

1. Down - provides the most warmth for the lightest weight. Down also remains the leader in compressibility and resilience.
   The major drawback to down fill is that once it is wet it does not provide warmth and it takes a long time to dry. Down bags also tend to be more expensive than synthetic bags.
2. Synthetic - keeps you warm even when it is wet and it dries quickly. Less expensive and more durable than down bags.
   The downside is the synthetic is heavier, bulkier and less compressible than down.