It is generally used in laboratories to cultivate bacteria, molds and other types of microorganisms. The bottom is usually covered with different culture media, depending on the microorganism to be cultivated.
If you want to look at colonies, during the incubation time of the microorganism sown in the plaque, it is kept upside down, resting on the lid. In this way, the agar remains in the upper sector and when condensing the water vapor generated by these microorganisms by their metabolism, falls on the lid, preventing the microorganisms from being diluted, keeping them fixed to the substrate.
PETRI boxes of Kalstein can be made of glass or disposable plastic. Crystal Glass should be sterilized before use in autoclave and wrapped in plastic wrap, plastic already come sterile and come in various sizes of capacity, the idea of plastic is that when you put them in the autoclave after use are unrecognizable and you can dispose of them properly. They can be used for the culture of bacteria mainly with agars (gelatins) and also for the culture of cells, in this case cell lines that adhere to the matrix that already comes in the Petri boxes.
Which one are you looking for right now, plastic or glass?