After each use, allow the helmet to air dry and then store it in a cool, dry place where it won't get damaged.
Note that excessive heat can damage your helmet.
For example, in direct sunlight a dark gear bag, the interior of a car, or an automobile trunk can get hot enough to cause heat damage (damaged helmets will appear to have uneven or bubbly surfaces). Therefore, when not being used for a period of time we recommend that the helmet be placed back into its box or case and stored in a cool, dry place.