Aromatherapy is a branch of herbal medicine that uses essential oil to achieve health benefits. The sense of smell, the strongest of all, is the only one that remains active while you sleep. Aromatic substances tend to be extremely volatile, which means they vanish quickly in the air unless kept in sealed containers that release them gradually. It is this principle that allows fabric to be used as an aromatherapy carrier.  Thousands and thousands of microcapsules are deposited between the fibres and become stably attached to them. During normal use of the  mattress, the body turning and pressing on the fabric causes some of the microcapsules to break, gradually releasing the essential oils inside. This goes on for a very long time, even after numerous washes, and provides a pleasant fragrance of freshness and sense of relaxation.