The Oasis guitar humidifier is designed to last a LONG time. HOWEVER, if the crystals inside the humidifier spill out, are lost, or cake up from disuse, this replacement kit is quite necessary. This kit contains a small package of Humigel™ crystals sufficient to refill 4-6 times, instructions, a .15 cc scoop to accurately measure the amount of crystals needed and a 10cc. syringe. We feel that including the syringe in this package will both reduce crystals loss and encourage the use of distilled water for filling the humidifier. The dry crystals should retain their potency for 5 years or more. One replacement kit should last for several years even if you have several humidifiers to refill annually.