On October 26, 1909, Frank G. Daggett and Edward G. Slinghart received U.S. Patent No. 938125 on a Hair Growing Device:

The patent explains “[a]s is well known, a fruitful source of loss of hair is the lack of ventilation or circulation of air within hats. The warmth of the head soon heats
the air within the hat and the presence of this warm air in contact with the scalp
causes the hair to lose its vitality and to fall out.”

The device comprises comprises “a receptacle having perforations therein and provided with means for attaching the receptacle to the body or crown of the hat, together with a sack or container for material in a dry or powdered form capable, when heated or moistened of evolving oxygen.” “In operation, the warmth and moisture of the head heats and moistens the air confined within the hat and gradually evolves oxygen from the ingredients contained within the sack.”