Soda-lime silica glass. These flat, clear Petri dishes will withstand repeated sterilisation (wet or dry). 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 sterilisation is routinely used. The covered dish is not airtight. Bottoms also have a triangular enamel reference point for serial dilutions.
Caution: These dishes are not designed for rapid thermal shock.