Humidifying liquids for cigars offer several distinct advantages over plain old distilled water. For starters, propylene glycol solution, or PG solution, is a thicker, more viscous liquid containing a half-and-half solution of propylene glycol and distilled water. This mixture is hydroscopic to 70% relative humidity, which means that it will only evaporate until the humidor's RH reaches 70%. It is advised to "recharge" humidification devices with PG solution every few months (depending on the manufacturer's instructions, of course). Humidifying liquids also include gels, which are disposable jars that take the guesswork out of maintaining proper humidity. Whichever humidifying liquids are right for your setup, you'll find the lowest prices online at Famous Smoke Shop.