Menthol is a natural extract from Peppermint oils. Traditionally used as incense and in liniments. How to use: add 1 tablespoon directly to the oil burner, fill the vaporizer with water and light a candle, and top up as the water evaporates. The same menthol can be used repeatedly provided the water is topped up. When the oil burner is not in use the menthol will re-solidify and look like an ice-skating rink. Either crack and remove or use again by lighting the oil burner again. Menthol provides a fresh, crisp aroma, particularly in colder seasons. You can also add essential oils to the oil burner at the same time if desired. Menthol varies from clumps to fine powder when sold.