The outer case is made of a sleek looking aluminum and inside is a "surgical sponge" material that wicks from the inside out.  It is a lower maintenance design than most passive humidifiers that will go longer between refills.  And, you only need to use distilled water!  No chemicals necessary to regulate humidity.  Durable black finish.  For larger humidors, please look at our other Paradigm models. Size:  3" W x 1 1/2" H x 1" TH