My husband works in the garage in all kinds of weather, making guitars and ukuleles. In the summer, to keep the sweat out of his eyes (and keep the sawdust out of his hair), he wears Ham Bag Hats. This started a long time ago and yes, it was really the muslin bag that hams come in. He has finally worn out/lost all his ham bags, so I made him some new ones.
The basic shape is how we remembered it to be- slightly asymmetrical. I cut out 2 pieces, serged them together and that was it.