Sometimes new hats -- and clothing in general -- just don't look right until they appear lived-in. Unless you buy one of the many pre-distressed hats that look as though you've owned it for a decade or two, you might want to accelerate the process. Any machine-washable hat, or one featuring a fabric that won't be damaged from heat and hot water, can be quickly faded, making it look like your go-to the first time you slip it on your head.
Rub on the sections of the hat with sandpaper that you want faded more intensely or quickly, such as the bill or front panel. Continue until these areas begin to visibly lighten.
Toss the hat into the washing machine on a warm setting. Throw it in with some old towels. The friction helps to rub some color away. Make sure there's nothing on the towels you don't want possibly transferring to your hat, such as oil and grease.
Add laundry detergent and a capful of bleach. This won't whiten the hat, but will definitely fade the color.
Toss the hat into the dryer on medium heat. The combination of heat, hot water and the tumbling action will have an immediate effect on color saturation and stiffness.
Hang the hat in the sun on a clothesline. The sun's rays are well-known for their ability to fade colors in car interiors and clothes left on a hook. This can be done wet or dry.
Rub the edge of your brim with a knife or scissors to fray the fabric, imitating years of use.
Never expose fabric to un-diluted chlorine bleach. In addition to possibly removing almost all the dye, chlorine bleach is notoriously hard on fabric fibers of all types.
Do not wash or dry a wool hat. Heat and hot water will shrink it, making it possibly unwearable. The same is true for cotton if dried on high for too long.