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If the sleeping bag gets dirty, wash it in a front-loaded washing machine. Run it through the dryer until completely dry. If you have a synthetic sleeping bag, check the tag for special instructions before you do this.  Down sleeping bags get clumpy in the wash. To make them even and fluffy again, add a tennis ball to the dryer near the end of the cycle. Never wash a sleeping bag in a top-loaded machine. The agitator may tear the fabric. Never store a sleeping bag while it is wet or even a little damp. If the sleeping bag doesn't need a visit to the laundromat, just spread it out to dry instead. Some people turn the bag inside-out and hang it so that the inside airs out (that's often what gets smelly over time). Storing a sleeping bag in a stuff sack may compress the material permanently (he stuffing inside can separate along where it's folded and this makes it colder and less warm to sleep in). Let it expand between trips with one of the following storage methods:  Place it in an oversize, breathable storage bag made from cotton or nylon. Spread it out under the bed. Hang synthetic (but not down) sleeping bags on a large clothes hanger. If you're storing your sleeping bag in a damp room, place it in a bone-dry, airtight tub. Keep it away from areas with a known insect problem.

Summary:
Wash the bag if necessary. Air out the sleeping bag after each trip. Leave it uncompressed during storage. Protect it from insects and water.