Do you send your wool coolers to a horse laundry for cleaning like a regular blanket?
Wool clothing items of my own I would dryclean, but a horse laundry doesn't use drycleaning chemicals, do they? Will a wool cooler shrink or be damaged by washing in (cold, obviously) water by a horse laundry service?
It's otherwise clean (hasn't been used yet), but got some mildew scent from being in storage. Is there a good way to get that smell out without laundering it? What about those *dryclean in your dryer* kits? Worth a try? I definitely don't want to ruin a new cooler.
I hung it outside in the sun for a few hours, which helped some, so maybe I need to do it again.
If they are not totally filthy (horse hair, mud, etc.), my regular dry cleaner will take in my wool coolers for the same price as they would charge for a comforter/blanket. They have always come back looking wonderful, and I never have to worry about damaging them by attempting to wash them myself.
If it truly IS mildew/mold, the ONLY thing that will kill the spores is bleach. I don't think you want to do that to a nice garment.
Earlier post that said rubbing & agitating wool is what makes it shrink & mat is correct-that plus water-and water is where mold grows.
So, my advice would be to brush the wool out with a stiff brush and lightly spritz with lemon juice to help kill off the mold spores and leave flat in the sun to dry. It's a less aggressive, less sure kill than bleach, but may work. NEVER wash wool horse clothing with ANY detergent, even Woolite.
If it's just the SMELL, then wrap the cooler up in a plastic bag with some coffee grounds. Even used coffee grounds (dried) will take the smell out of anything.
I keep pomanders of used coffee grounds in garment bags for velvet dresses & such to fumigate after a party where smoking is allowed. They work wonders for old furniture drawers too.