This hat is very well made and has a soft fleece lining. My head is on the smallish side -- yet is jam-packed with brains, of course -- and this hat fits my small head without being too loose and falling off or constantly listing at a jaunty angle, but the fabric is stretchy-ish so I think it would likely fit a medium adult head as well.

It also makes people smile, and i like that very much. A satisfying millinery experience all around.