What role does the stacking structure, crafted so that the container bottom and lid interlock, actually play when in use?

The bottom surface is recessed inward and the lid has a raised rim upward. They stack upward stably. Toyo Sasaki's glass round food container is designed so that the bottom surface and the lid interlock without spinning loosely, preventing it from slipping sideways when stacking bowls in multiple tiers on refrigerator shelves^[1]. With this craftsmanship considering everyday usability, it received the Good Design Award in 2010^[2].

However, the characteristics of the lid must be taken into account when stacking and storing. The lid material is polyethylene, and the temperature it can withstand is up to 60℃^[3]. If you put in hot food immediately after cooking and close it right away, the lid may warp due to the heat and the interlock may become loose, so you must always stack them after letting the steam cool down sufficiently before covering.

hmmm, the structural convenience of stacking neatly is properly maintained through the small habit of watching the lid's temperature to keep its shape.