Depending on the material that a hat is made of, they could be thrown in the wash with other delicates on a low rinse cycle. However, hats that have more of a shape to them, or are made of a special material (e.g. brimmed hats or fax fur hats), you’re better off spot cleaning them; you don’t want to risk being a hat out of shape or tampering with its material. If the base is sheepskin, it's best to go to a specialty leather cleaner.