Martin Humidifiers are made from the finest materials available. The tubes are extruded from the finest non-vinyl and non-allergenic resin, soft enough not to exert pressure around the sound hole and are sufficiently sturdy to minimize contact with the insides parts of the guitar. The water suction stem within the Martin humidifier absorbs ten times its weight in water and slowly emits moisture through the holes. MFSKU 18AHG UPC 729789347556