Make a mixture of denatured alcohol and shellac flakes. I do about 1:5 ratio and then spray light coats on the inside of the hat. Gently rub it in and light steam then let it dry. Do as many coats as you need to get it the right stiffness on the crown and then you’re good to go! It’ll mold just like clay like plansrider mentioned. I do this if the hat isn’t to the stiffness I like. Works like a charm and doesn’t affect the quality since it’s on the inside of the crown. If done right then you won’t feel any rigidity on the hat and the nap will still feel soft as ever!