The Boveda Fabric Holder safeguards your stringed instruments from humidity-related deterioration by securing two-way humidification pouches within your case. Wooden instruments demand stable moisture levels between 45-55% relative humidity to prevent cracking, warping, and structural compromise. This holder's leak-resistant design facilitates controlled vapor exchange while shielding your instrument from direct contact with strings and impact damage. The soft polyester construction poses no risk to instrument finishes. Compatible with the complete Boveda humidification line, including high-absorbency formulations for humid environments, this holder accommodates standard packs and enables musicians to deploy dual units for enhanced climate regulation. Ideal for violin, viola, and cello cases. Replacement packs sold separately.