In addition to washing my hats with a hat rack, I often wear a bandana or hat liner to keep sweat from entering the hat in the first place, this prevents stains and odors and extends the life of the hat. Any bandana will work, but if you want something more substantial, I use a product called CrownWear (www.CrownWear.com) that a friend recommended. He uses it under a bike helmet, but it works great under my ball cap, even in the Arizona summer.