You should always start by reading the manufacturer’s recommendation (on the tag or online). But, in general, the answer is yes, sleeping bags are machine washable. You don’t need to wash your bag obsessively, but once a year is a good idea.
These tips will have your bag smelling fresh in no time.
Get yourself some Nikwax Down Wash Direct. It’s made specifically for washing down sleeping bags and jackets. It works on hydrophobic and non-hydrophobic down. According to the brand, it will restore and even add water repellency while maintaining fill power and insulation.
Go to your closest laundromat. Don’t use a typical home washing machine with a central agitator. You want one of the big, front-loading washing machines that wash by spinning vertically.
Remove detergent buildup from the detergent dispenser on the machine. It’s a pain, but bring a couple of old towels to do the job. Or try to find a clean one.
Place a maximum of two items in the washing machine.
Add 100 mL of Nikwax Down Wash.
Wash according to the label if it has one. Generally, use a low setting and slow spin.
Run multiple spin cycles, each time incrementally increasing the spin speed, to remove excess water.
Dry in the dryer on low heat. Toss in a tennis ball to help refluff the down. Check regularly and tease out stubborn clumps by hand.