Sterile and made of polystyrene. Accommodates deeper fills for longer culture periods. Used for fungal cultures, plant propagation. Has three venting ribs into the underside of the lid to prevent condensation build-up.- Petri Dish & Pads, 9 x 50mm, Frosted Top Permits Labeling, 20/slv, 25 slv/cs 14-21 Days