Washing will change the shape of baseball caps.
Washing will wreck the brim on baseball caps.
Shrinkage - it was funny on Seinfeld but it is NOT funny when it comes to your favorite baseball hat.
To start with, have a look at the little tag (usually on the inside edge) that tells all about what your baseball hats are made of and what the manufacturers instructions are for washing the baseball hats. If the tag is still there and you can read it that's great. Now you have some of the information you need to go ahead and wash your baseball cap safely, without shrinking it or wrecking the brim.
But if your baseball caps tag is gone or unreadable, or if you have some really old baseball caps that never had a tag (pre 1983), then extra care is required when cleaning. See CLEANING OLDER BASEBALL CAPS below.
Cotton, wool or jersey, what are your baseball hats made of?
Cotton twill is strong and durable and has that "cotton" look to it - the older it is the better it looks
Cotton polyester blends are tough, bright and usually colour fas
Jersey mesh is a durable, colorfast knit that is easy to wash
Wool is warm but can shrink in water and/or heat situations - see CLEANING WOOL BASEBALL CAPS below.
Lets say that you have fairly new baseball hats made out of cotton, a cotton blend or jersey knit. Washing them should not be a problem. Most baseball hats today use a plastic form to shape the brim, not cardboard. The plastic can withstand a wash with no deformation.
So if your baseball caps have been made in the last ten years and are made out of one of the above materials (except wool), just spray any dirty areas with a prewash spray (Pre-treat the liner or headband with a enzyme based laundry pre-spray before washing) and simply toss them in to the clothes washer with the rest of your clothes (similar colours, cold water wash if possible, warm if you have to, hot - no way! ALSO NO BLEACH)
If you want to hedge your bets and be extra careful you can get one of those plastic forms for baseball hats, strap your hat into it and then throw it into the washing machine. After the wash let your baseball hats air dry. Couldn't be simpler.
Using Dishwashers? You may run across information that infers it is OK to wash your baseball caps in the dishwasher.
(Including "I have also seen a cap frame which you can purchase for the dishwasher which holds the hat in place for washing in the dishwasher - again removing after the wash cycle and air dry." OR "To clean baseball caps without destroying their shape, place them on the top rack of the dishwasher and run through a complete cycle.")
This is not recommended. Dishwashers are for dishes, clothes washers are for clothes. When was the last time you ate a meal out of one of your baseball hats?
If you have a reason to doubt whether your older baseball caps have a plastic brim and if you would be devastated if anything happened to them then err on the side of caution, see CLEANING OLDER BASEBALL CAPS next.
How to clean your older baseball caps without actually washing them
First do a colorfastness test, take a wet washcloth with a little mild detergent (Zero or Woolite are both mild) and a little 'Spray and Wash' on it and rub it gently on a hidden spot on your baseball caps inner rim. Rinse by rubbing with a clean wet cloth and air dry.
If there is no change to the colour then go ahead and clean the dirtiest part of your older baseball hats, the headband, using the washcloth and detergent.
After you have sufficiently cleaned the headband of sweat stains and soil, rinse the washcloth with clear water and once again wash down the headband, cleaning up any leftover soap. Air dry and your baseball caps will be ready to go again. Some sweat stains remain but at least the baseball caps will be cleaner with no risk to the brim.
Hand wash in the sink with cool water and a mild laundry detergent meant for wool, like Woolite or Zero.
Be gentle with your wool baseball caps, if you scrub, rub or twist you'll cause the natural wool fibers to matte together and you will end up with felted baseball hats that are a couple of sizes too small for you. Rinse well in cool water, roll gently in a towel to remove most of the water then reshape your baseball hats and allow them to air dry over a coffee can or some other head shaped object.
If you dry your wool baseball hats on your head, they will shrink precisely to the size and shape of your noggin.