I can only speake to dry heat , I know some use boiling water or I have seen oil used to, I'm assuming your talking for straitening the horn when horn gets thinner it bends fairly easy with minimal amounts of heat, In the pics when straitening I used a laser thermometer and never broke 110 F but used less where needed for very short periods of time it bends easy and little heat is needed I also at times wrapped the horn strips in a electric blanket before heating and bending one of the techniques in Adams book , to much heat and you can ruin the horn compretion qualitys !