Key takeaways
- Leak-proof lid with gasket: essential for soups in a work bag or backpack.
- Wide mouth: easier to fill, eat from and clean.
- Folding spoon in the lid: handy when you forget cutlery.
- Lid that doubles as a bowl: useful for sharing or cooling food.
- Dishwasher-safe parts: check whether the body or only the lid is dishwasher safe.
A good insulated food jar turns last night’s soup, chili or pasta into a hot lunch at work or school, without a microwave line. The best ones keep food hot for hours, do not leak in a bag and are easy to eat from and clean. Here is how vacuum-insulated food jars compare by size, shape and features, and how to get the longest heat retention from any of them.
How insulated food jars work
Most food jars use double-wall stainless steel with a vacuum between the walls, which slows heat transfer. The lid is where most heat escapes, so jars with thick, well-sealed lids hold temperature longest. Wide mouths make eating and cleaning easier but lose a little more heat than narrow openings.
Sizes compared
| Capacity | Fits | Best for |
|---|---|---|
| About 10 to 12 oz | A child’s portion | School lunches |
| About 16 oz | One adult serving of soup or pasta | Office lunches |
| About 24 oz | A large meal or two small portions | Big appetites, long shifts |
| About 32 oz and up | Family portions, stews | Job sites, road trips, sharing |
Fill the jar close to the top; an almost-full jar holds heat better than a half-empty one. Compare vacuum-insulated food jars by capacity.
Features worth having
- Leak-proof lid with gasket: essential for soups in a work bag or backpack.
- Wide mouth: easier to fill, eat from and clean.
- Folding spoon in the lid: handy when you forget cutlery.
- Lid that doubles as a bowl: useful for sharing or cooling food.
- Dishwasher-safe parts: check whether the body or only the lid is dishwasher safe.
Keeping food hotter for longer
- Preheat: fill the jar with boiling water, close it for 5 to 10 minutes, then pour it out.
- Heat food until steaming hot before packing it.
- Fill to near the top and close the lid quickly.
- Keep the jar in an insulated lunch bag, away from cold drinks or ice packs.
Food safety
Food safety guidance recommends keeping hot foods at 140°F or above. A well-preheated jar filled with steaming food can stay hot for several hours, but heat retention varies by product and conditions. If food will sit longer than the jar can keep it hot, pack it cold with an ice pack and reheat it instead. See insulated lunch bags that fit food jars.
Cold foods too
The same jars keep yogurt, fruit, salads and cold noodles chilled. Pre-chill the jar with ice water before filling for best results.
Meals that travel well
Soups, stews, chili, curries, mac and cheese and pasta with sauce hold heat well and taste good after a few hours. Crispy foods turn soft, so pack crunchy toppings separately.
Common mistakes to avoid
- Skipping the preheat step, which loses a lot of heat in the first hour.
- Packing food that is warm rather than steaming hot.
- Putting a non-dishwasher-safe body in the dishwasher, which can damage the vacuum seal.
- Choosing a jar too large for the portion, leaving a lot of air inside.
Which jar suits you
School lunches: a 10 to 12 oz jar with an easy-open lid. Office soup: a 16 oz leak-proof wide-mouth jar. Long shifts or job sites: 24 oz or larger. Sharing or road trips: a large jar with a lid that doubles as a bowl.
FAQ
How long does a food thermos keep food hot?
Often several hours when preheated and filled with steaming food, depending on the product.
Should I preheat a food jar?
Yes; filling it with boiling water first makes a big difference.
Can I put a food thermos in the dishwasher?
Some lids and bodies are dishwasher safe; check the manufacturer’s instructions.
What size food jar for an adult lunch?
About 16 oz for one serving; 24 oz for larger appetites.
