U-Konserve's stainless steel leak-proof insulated food jar with an all-stainless interior keeps food hot or cold for hours! Pack soup or chili in the morning and lunch will be steaming when you are ready to eat. Pack smoothies or yogurt and it stays cool until lunchtime. Take leftovers on-the-go so you can eat healthier and reduce food waste with our double-walled food jars. Similar to a thermos, the Insulated Food Jar keeps the temperature you start with, so pre-heat with very hot water for a few minutes before adding piping hot food, and pre-chill in the freezer for a few minutes (lid off) before adding cold food. Our food jars keep pre-heated food hot up to 5 hours, and pre-chilled food cold at least 8 hours.