Apologies to anyone who has posted this tip before but I've just discovered it and it really works. To get rid of a smoky or musty smell in a hat, get a couple of those fabric softener sheets that go in tumble driers and put them in the hat. Tie it up in a plastic bag and leave it for a couple of weeks. Result - no more nasty smell. I've just done it with a 1930's flying helmet that I got on Polish eBay. When it arrived, it smelt like a combination of wet dog and bus station ashtray. But no longer. PLEASE NOTE THAT THE SHEETS YOU USE MUST HAVE BEEN USED IN THE TUMBLE DRIER FIRST BECAUSE UNUSED ONES CONTAIN AN OIL THAT LEAVES MARKS ON THE HAT.