Humitrons are made of the most advanced material available. The tubes were custom extruded of the finest non-vinyl and non-allergenic resin, soft enough to exert pressure around the F-holes/sound-holes and sufficiently sturdy to minimize contact with the inside parts of an instrument. Our water-suction stems within the Humitrons absorb water ten times their weight and then slowly release it through the holes.
To determine when to use Humitron, listen to your local weather forecasters. When the humidity falls below 50% it is time to use Humitron by simply submersing it in *water for several seconds, and while removing it, wipe the excess water off and place Humitron inside. Also bear in mind that the driest months are in the winter season and in the places where rain falls are low and temperatures are high. We do not offer any color changing type moisture indicators since they only function on a relative humidity scale and become totally obsolete when the air is saturated with 90% water.
*try to use distilled water when soaking the Humitron since one rich in minerals will gradually diminish effectiveness of the water absorption stem.