Boveda Small 2-way Humidity Control Kit Features: Maintains a relative humidity of 40%–50% when placed with your instrument in a closed case Prevents warping, shrinking, and cracking to preserve the look and tone of your instrument Small kit is ideal for for electric guitar, bass, mandolin, ukulele, violin, clarinet, and more 2+ year shelf life in original packaging Once the packs become rigid, simply replace with Boveda refill packs (sold separately)