As used by Taylor guitars (and our own repair department!), the RDM Humitrons are made of the most advanced material available. The tubes are custom extruded of the finest non-vinyl and non-allergenic resin, soft enough not to exert pressure around the F-holes / sound-holes and sufficiently sturdy to minimize contact with the inside parts of an instrument. The water-suction stems within the Humitrons absorb water ten times of their weight and then slowly release it through the holes. 

We highly recommend the RDM Humitron for safely rehydrating guitars damaged by lack of humidity, or for storing guitars in dry climates.