Look up the brand of sport wash called Atsko. It’s the same company which makes the orange capped waterproofing spray which can be found at Wal-Mart mentioned in another post. They have sport wash which works on rain jackets, down coats, and any waterproof breathable materials, like most horse blankets. They also have a wash specific to horse blankets. It is not very expensive when you compare it to having to buy a new blanket due to ruining the w/b barrier. In most cases I know of the w/b barrier actually works better when it’s clean–but you really have to use the correct type of wash, since detergents can ruin the w/b abilities of some materials–and some of the membranes actually improve and are reactivated when dried in the drier. So know what’s in your blanket. Do some research on re-waterproofing rain coats or tents and you’ll find that cleaning them properly often returns the waterproofing. Atsko also sells water resistant sprays and water proofing sprays. Some are breathable some are not, so be aware of what you are sealing/ spraying your horse blanket with before you do so. Most horse blankets are waterproof BREATHABLE, not just waterproof. Good luck!