The basic idea
The outer pot is kept damp, the inner pot holds the food, and the sand between them stores water. As water evaporates through the porous clay, heat leaves the system and the inside can become cooler than the surrounding air.
Where it works best
Evaporative cooling works best with airflow, shade, and drier air. It is a low-energy cooler rather than a powered fridge, so results depend on the weather and setup.
Why build one as a kit?
The kit makes the principle tangible. You can assemble the cooler, see how the sand and pots fit together, and learn why a traditional idea still matters for low-energy living.