Hats must not be washed or dry-cleaned.  If your hat gets dirty use a
damp cloth to clean it and shape it back to its original shape. 
Allow to dry. Felt hats can also be brushed lightly with a soft brush.  To
do this place the hat on a plastic head or somewhere flat with the
edge of its brim up.  This is particularly important for wide-brimmed
hats. When not in use hats should be protected
from dust and stored in a box or cabinet. 
Hats are not water resistant. If your hat gets wet, turn it upside down and allow it to dry properly. 
Be aware that summer or formal straw hats cannot withstand water.