The HC26E1004 water panels have an Agion® antimicrobial coating. Agion incorporates silver that naturally inhibits bacterial growth. Silver is proven to be safe and non-toxic.The Honeywell HC26E1004 water panel is made of layers of an aluminum mesh with a porous pumice-like coating. The coating allows the water panel to absorb water, but without it the water would bead up on the aluminum and the evaporation would not be as effective. The water panel is made to last last one season.