To answer this question, you have to know how the mushroom packaging is made first. In short, it is using crops waste as structure substrate and adding special fungus to develop its mycelium to combine all raw materials and solidify together in the mold. Usually, the mold is vacuum formed mold and the mycelium grow in the mold to expected dimension and shape. This process usually takes 3 days, then we remove the formed mushroom packaging from mold and dehydrate it. You can understand the shape and dimension of the mold decide the final mushroom packaging.
Talking from the production aspect, there is indeed a size limit for the cut-out tray for mushroom packaging like below. It is at least one dimension is less than 21.5″ among the 3D dimension of a tray.
