In the unglazed format, the surface of this ceramic diffusor is porous in nature, which makes it absorbs liquids/essential oils over time and so aroma persists longer time and less volatile. There is no need for extra heating for this unglazed ceramic diffusor. Ideal for small spaces in the bedroom, lightweight to carry. Only one type of essential oil at a time. ⚠️Easy to clean the surface, using water to wash off the remaining essential oils or dust, and cotton swabs to wipe down the rest. However, stains and grease are hardily removed.