How to choose a sleeping bag

1. What temperature rating is right for me? Look for an ISO (International Standards Organization) rating (formerly "EN" European Norm was used, which is similar). There is a "comfort rating" at which temperature where you are likely to be comfortable if you tend to be on the colder side, and a "lower limit rating" which is the limit where someone who doesn't tend to get cold easily will probably be okay. Note, the number in the bag name may not be the true temperature rating.

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2. What fill do I want? Down bags tend to be the lightest and most compactible bags relative to warmth, but typically at a higher price, and some people are allergic to down. Also, you must keep down dry, if it gets wet it looses its ability to keep you warm. Synthetic fill bags are relatively warmer when wet, and modern synthetics are lighter and more compactible than in days past, but remain usually heavier and larger when stuffed. Down also has different "fill power" ratings, the higher the number the higher the relative quality and cost. A 950 fill bag will compact smaller than an equivalent 650 fill bag, but at a higher price.

 

3. What shape do I want? Most commonly scouts use "mummy" style bags (first photo above) or rectangular style bags (second photo). Rectangular bags are roomier, but less thermally and weight efficient. Rectangular bags are more common for summer style bags, but might be a good choice for you if you don't like the restricted feel of a mummy style bag which is conformal. The mummy style, often with a built in hood, gives you the most warmth for weight and is most common for a 3 or 4 season bag. If you are into ultralight gear, you may also want to research camping quilts (third photo), which usually require pairing with an air mat, but can save ounces when you are going for the lightest setup possible.