Musty Smell in Comforter

Both vinegar and baking soda will work but it's not good to use them together, because they cancel each other out. Vinegar is an acid and baking soda is a base, try putting a couple of tablespoons of each in a bowl. They foam like crazy when put together.
I would wash in laundry detergent with baking soda added and then add vinegar to the rinse, vinegar also cancels out detergent. Then hang in the sun until dry. If the musty smell is still there keep putting it outside in the sun. One run through the washer with vinegar or baking soda killed any mold or mildew, it's just the smell that lingered. Sunshine is the best way to get rid of mold and mildew smells.

I don't think the vinegar can hurt the fabric so I'd try too. If it doesn't work, you can find dry cleaners who will launder comforters for $15- $25.

First, hang it outside for a day. Let it really get aired out.

Then bring it back inside and wash it once in warm water with a scoop of oxy clean, and then again with vineger. After the vinegar wash, rinse it twice. Be sure it gets straight into the dryer and does not sit in the washer.

I had two quilts that came from my ex-MIL's house. She smoked like a chimney. The blankets stunk like smoke (and were YELLOW!) and smelled musty. The above regimen took the smells and stains right out.

Vinegar. I have a comforter that had been in our basement for 2 years and had that "basement" smell. I washed it regular and still had it. Then I washed with some vinegar and let it soak a bit. The smell came out after teh second time. i guess because it was so long it needed a bit extra.

Try it for sure. Let it air out.....I don't know your weather but how about putting out side to get the fresh breeze through it? If a dry cleaners doesn't work either I wouldn't hang onto the comoforter...there's obviously mildew or mold through the fibers which can't be god for your breathing.

baking soda and vinegar with cold water

I use vinegar in my daily loads, so I don't think it will hurt the fabric (unless it says dry clean only).

I use Downey on all sheets and blankets. Makes them smell great for weeks and softer too.

I would wash it with Sol-U-Mel in the load.

I've heard good things about vinegar getting odors out. I know it gets urine odors out and I have heard of it getting out mildew stains. It can't hurt to try.