Bickmore Products. Kahl's was originally developed in the early 1900's to duplicate the process of hat stiffening that was performed when the hat was originally produced and shaped. It is very versatile in that it can be used on any quality hat and will not affect additional shaping and cleaning at a later date. Kahl Hat Stiffener contains no fillers or synthetic substitutes that can turn light-colored hats yellow. Because of the slow drying time, no chemical residue is left to attract dirt. Kahl Hat Stiffener out performs all other hat stiffeners in both stiffening and gentleness on tone and texture. Available in 8 oz and gallon sizes. Due to the weight of the gallon size, there is an additional fee of $4.50 added to the normal shipping charges for the gallon size.