I haven't tried methol in balms yet. I've used up to 3% flavor oil for balms, but would try 1% or less for a stronger oil like menthol. It's alot easier to add flavor oil than to realized that you added too much. Just my opinion. I pour balm into a clean wide-mouth half-pint jar. Then put the jar on a candle warmer to keep it liquid while filling tubes up. To fill the tubes, I use a pipette. I haven't tried the microwave yet for melting balms.