The internal retention material can hold up to ten times its weight of water releasing it as a vapour through precision vents cut along the length of the tube. Tubes are extruded from non-vinyl and non-allergenic material. Water absorbtion stems inside Humitrons are sized for each class of instrument. End plugs are sealed to prevent dripping. Caps are designed for each instrument to keep Humitrons in position. Quantity and size of holes are calculated for gradual and effective release of moisture. Tubes are flexible to place Humitrons easily inside instruments and rigid enough not to lay flat. Made in USA by RDM