Minimize moisture loss in your terrarium with ZooMed's Humidity Plus Silicone Terrarium Cover. Trim to fit any size, this terrarium cover is non-toxic and is made from a high heat tolerant material. To use: Lay on top of terrarium screen and mark placement of lights, heaters, and ventilation with a ball-point pen. Cut to size. Place on top of existing terrarium screen. Do not place lamps or heating elements directly on top of silicone mat. This item will reduce ventilation – be sure to leave appropriate space for fresh air. 16" x 16"