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 50 cigars your humidor can hold, plus one additional packet (for example, 2 packets for a 50 cigar humidor, 3 packets for a 100 cigar humidor). Each set will last 3 months in most humidors. Shelf life: 2 years inside the plastic wrapping.This product comes in three presentations. You can buy the single packs individually wrapped in plastic. The 12-pack refill has 12 individually wrapped large 60 gram packs of Boveda 75%. The Bulk 20-Pack brick saves you the most money as each Boveda is not individually wrapped in plastic, instead the 20 large 60 gram packs are packaged in a resealable plastic brick. The bulk pack also saves you time as there is no need to unwrap each unit.