We typically recommend soaking fabrics in MiraZyme to eliminate odors. However, in order for MiraZyme to be effective, you need to allow the sleeping bag to air dry. In general, you cannot properly air dry a down sleeping bag. If you did, the down would begin clumping together and the bag would begin to lose loft and warmth. To remove odors from your sleeping bag, start by cleaning and drying the bag first. Find directions here.
If that does not help, soak the bag in MiraZyme.
Step 1: Fill a tub with just enough cool water to submerge the sleeping bag. Add 1 oz of MiraZyme (depending on odor strength) for every 5 gallons of water. Stir to mix.
Step 2: Unzip all zippers. Submerge bag in solution saturating inside and out. Soak for 10 minutes then remove. Do not rinse, the microbes do much of their work while the item dries.
Step 3: Once the item has completely air dried, dry the bag in a large commercial dryer on the permanent press (medium) heat setting or according to the manufacturer's recommendations. Clean tennis balls may be added to break up down clumps.
NOTE: Home dryers aren’t big enough to let sleeping bags tumble freely. The bag needs to be lifted and then free-fall to dry properly. High heat or small home dryers can melt synthetic fabrics. Always use a commercial dryer.
A few tips regarding MiraZyme:
As soon as you mix MiraZyme with water, this activates the microbes. At that point, the microbes begin eating away at themselves and odor causing bacteria. MiraZyme is most effective immediately after it has been mixed since most of the microbes are still alive. As time progresses they consume themselves and the solution becomes less effective. Make sure that you are soaking the item immediately after mixing with water and you are not using an older mix or pre-mixed solution.
Also, the longer the item is able to air dry, the longer the microbes are able to do their job. Heat will kill the microbes and rinsing will wash them away. Do not rinse the item once you have soaked it and try your best to dry the item in a cool environment out of direct sun light.