You can always clean your horse fly mask by hand if you choose, however; many horse fly masks nowadays can be put in a washing machine. You will need to check the label of whichever one you choose to purchase and follow the care instructions included with your horse fly mask. During warmer months, you can also hand wash and air dry your horse fly mask. Be sure to use mild detergents and be mindful of your horse's allergies if any are known. If you notice your horse has an irritation after the washing of the horse fly mask, remove it immediately and try washing it in a different, milder soap. There are soaps designed especially for washing horse fly masks, just check your local horse supply store for their recommendations.