Bickmore Kahl Hat Stiffener 10FPR131 The Original Felt Hat Stiffener. Khal Hat Stiffener will restore body and shine to an older felt hat. Kahl Hat Stiffener will not affect the tone, texture, or color of the hat. It will not turn yellow or flake off. Kahl Hat Stiffener will not affect future hat cleanings, shapings, or reblocking. 8FL oz Spray