We have tested the ColdKit in combination with the PlanetBox lunchbox and Carry Bag on a typical school day. By pre-cooling the PlanetBox in the refrigerator overnight and then placing it inside the Carry Bag with the ColdKit in the morning, a substantial lowering of temperature can be maintained. The exact temperature maintained throughout the day will depend on the ambient temperature the PlanetBox is stored in for the morning, exposure to direct sunlight or shade, and the number of times the lunchbox is opened throughout the morning.
In our tests, a consistent 40° F temperature was maintained inside the lunchbox while the exterior temperature was 75° F through the morning hours. 40° F is a safe temperature to store perishable foods, according to the USDA. If a significantly higher exterior (ambient) temperature is anticipated, then we would suggest using two cold packs – one placed below the lunchbox and one placed above – to sandwich the PlanetBox in a blanket of cold throughout the morning. As reminder, the ColdKit can only maintain the cool for as long as it remains frozen. To truly keep perishable foods from spoiling for long periods, store them in a refrigerator.