Corning 3160-101CO PYREX® Petri Dish Covers Only will withstand repeated sterilization (wet or dry). The covers are clear, flat and marked in blue enamel. The edges are beaded to provide greater mechanical strength. The bead also provides a means to equally space the side walls of the bottom and cover, thereby reducing the capillary action of the condensed moisture on the sides. They are not affected chemically or thermally by any of the methods commonly employed in laboratories where sterilization is routinely used. The covered dish is not airtight. Packed 12 covers per case.