How to Choose a Sleeping Bag for Three-Season Camping

Sleeping bags are one of the few pieces of gear where the marketing language is almost useless. A bag labeled "20 degrees" might keep one person warm at freezing and leave another shivering at forty. The rating is a starting point, not a promise. Understanding what goes into that number helps you pick a bag you will actually sleep in.

The two big variables are fill and shape. Down fill is lighter and more compressible for the same warmth, but it loses insulation when wet. Synthetic fill is heavier and bulkier, but it keeps working when damp. For three-season camping in most climates, either can work. If you camp in wet, humid places and worry about a soaked bag, synthetic is the safer bet. If you want to save weight and space, and you keep your bag dry, down is hard to beat.

Temperature Ratings and Comfort

The temperature number on a bag is usually a lower limit, not a comfort rating. That means a 20-degree bag is designed to keep an average sleeper alive and roughly warm at 20 degrees, not cozy. Most people sleep comfortably about ten degrees warmer than the rating. If you tend to sleep cold, add another ten degrees of margin.

Other factors matter as much as the number. What you wear to bed, what you eat before sleep, and how well you insulate yourself from the ground all change how warm you feel. A sleeping pad with a good insulation value is not optional. The ground will pull heat out of you faster than the air will. No bag can compensate for a cold pad.

Shape is the next decision. Mummy bags are the most efficient: less space to heat, less weight to carry. The trade-off is that they feel restrictive. Rectangular bags are roomier and better for car camping, but heavier and less warm for the same rating. Semi-rectangular bags split the difference and are a good choice for most three-season backpackers.

Fit, Features, and Care

Fit matters more than most people think. A bag that is too large has extra air to warm, and a bag that is too small compresses the insulation and creates cold spots. If you are between sizes, size up slightly for shoulder room, but not so much that you rattle around inside.

Look for a draft collar around the neck and a draft tube along the zipper. These small features make a real difference on cold nights. A hood that cinches down is also worth having. Zipper quality matters too — a snagging zipper on a cold night is a special kind of misery.

Store your bag loose, not stuffed, when you are not using it. Compressing insulation for months shortens its life. Wash it rarely and gently, following the maker's instructions. A well-cared-for bag can last a decade or more, which makes the upfront cost easier to justify.