Boveda's 2-way humidity control is the only technology that can be pre-formulated to a specific humidity level with an accuracy of +/-2%. Boveda guarantees a constant level of humidity that never fluctuates or cycles. It also eliminates bacteria, mold or mildew. You will never have to use distilled water or PG solution again. Use one packet for every 25 cigars your humidor can hold. (for example, 2 packets for a 50 cigar humidor, 4 packets for a 100 cigar humidor). Each set will last 3 months in most humidors. Shelf life: 2 years inside the plastic wrapping. The 12-pack refill has 12 individually wrapped large 60 gram packs of Boveda 72%.