hat spray sits in tackroom and is used after every ride. if it's really sweaty i scrub it with a nailbrush and hot water, dab with a clean towel, then leave to dry naturally. i am fanatical about rinsing hairnets too now which had never occurred to me before, getting a bit OCD!
btw this way, they never get stinky/sweaty...
You can buy hat cleaners and deodoriser but I find if they are grubby normally from make up or s bit sweaty . I bought antibacterial wipes and use one of these even if hat looks clean its amazing what comes off and the bonus is hat is dry . Just keep a pack in grooming kit as useful to have
Was told by a staff member at our local saddler that the anti bacterial boot deodorising spray is the best thing to use. Just give a quick squirt after every use.
I've found the Charles Owen hat cleaner quite good, but it's best used regularly before the hat gets too stinky, if you've got a real ponger it might be a lost cause!