Some lunch boxes will be perfectly washer or dishwasher-safe. But, for the ones that are not, you are going to need to hand wash them. Thankfully, this is a very easy process and you eliminate any chance of damaging the material via machine-washing. Firstly, fill your sink with warm water and add a small amount of detergent inside. If the lunch box is waterproof, which will vary from model to model, go ahead and completely submerge it in the soapy water.
Then, it is time to get your hands dirty and unleash some elbow grease. Simply scrub the interior and the exterior of the lunch box with a soft cloth. If you can’t submerge it underwater, be sure to wring the cloth out before using it so no excess water gets inside. To rinse it, wipe it off with another cloth filled with regular water. To cap it off, hand-dry it with a towel and then allow it to air-dry until it is completely dry.
Outside of being handy for instances where accidental water is spilled, a waterproof lunch box also makes cleaning them immensely easier.