This humidifier is filled with a special hi-tech gel capable of absorbing 450 times its weight in fluid! When dry, the gel looks like sea salt. When fully charged, the gel looks like large chunks of gelatin. Best when used with Madeleine Propylene Glycol solution. Convenient for humidors up to 100 cigars in a volume of 850 cubic inches. A steel and magnet attachment system keeps the humidifier firmly attached to your humidor lid. The Crystal Gel shrinks as it loses moisture telling you exactly when it's time to refill! Measures 3 3/8" diameter x 7/8" thick.