Warm up/cool down the container beforehand: fill with boiling/cold water, close the lid and leave for 30 seconds at least. Then push the steam release first before opening the lid and emptying out.
Fill the bento box with very hot/cold dish. Should it be reheated before being placed in the container, prefer the use of a saucepan to the microwave for a more homogeneous temperature and result.
Fill the container completely: the insulating efficiency is best when the container is full.
Close the lid quickly and tight after filling container: to limit heat/coldness loss.
Do not open the bento box before your meal: every opening causes a heat/coldness loss.
Favor food with small pieces to big chunks.
Store your bento box at room temperature (21°C – 69,8°F minimum) to keep your food warm/in a cool place (15°C – 59°F maximum) to keep your food cold.
Mix the food before tasting to ensure a homogeneous temperature.