A comforter’s filling, rather than its construction, is the main thing that dictates whether it’s machine washable. As a general rule, down can’t get wet because water can cause the individual down feathers to clump and lose their warmth; so, down comforters should be dry cleaned. Other fabrics like cotton, polyester, wool, etc., are usually more forgiving. Check the tag for care instructions if you have a down-alternative comforter. Most of the time, you can toss these in the washing machine and the dryer.