5 Best Thermoses of 2026, Tested and Reviewed

Tested by Jessica Harlan

If you've ever enjoyed warm soup in your packed lunch, a swig of ice-cold water during a hike or a sip of hot coffee on a long road trip, you probably already appreciate the power of a good thermos.

These insulated food and beverage containers owe their technology to Scottish scientist Sir James Dewar, who invented the vacuum flask when he put one glass container inside another, creating a partial vacuum that kept the contents of the jar at a steady temperature for hours. It was in the early 1900s that this concept made the leap from the lab to home use, and the American Thermos Bottle Company began making insulated food and beverage jars. Originally a trademark, the term thermos is now used generically for any vacuum-insulated vessel.

Not all of the thermoses we tested have actual vacuum insulation, but they still could effectively retain temperature. "Even without a vacuum, two walls trap a layer of still air,” explains Dr. Taylor Wallace, CEO of Think Healthy Group, LLC and an Adjunct Clinical Associate Professor in the School of Medicine and Health Science at George Washington University. "Air is a poor heat conductor, so that gap reduces condensation. Keeping the air relatively still also limits convection currents. It's the same principle as double-pane windows or layered clothing."

Today's thermoses come in a range of styles, sizes and colors, but their design is typically similar: lightweight metal has replaced glass for the double-walled design with a screw-on lid that creates a temperature-stabilizing vacuum. A good thermos can keep soup, stew or coffee warm for hours, or can keep water, yogurt, or other cold foods and drinks chilled. Not only does this make for a more pleasant eating experience, but the most effective thermoses can keep foods at the optimal temperature to prevent bacterial growth and spoilage. Known as the "danger zone," the temperature range above 40°F and below 140°F is when conditions are favorable for bacteria to multiply most rapidly, which can cause illness.

Thermal vessels have another benefit, though. Using these containers to transport food and drinks from home can reduce waste and save money, cutting down on the need to purchase single-use containers. After testing nine insulated food jars and nine insulated beverage containers, we found some standouts that effectively kept their contents warm or cool and were convenient to use and transport.

How We Tested

We purchased 18 thermoses, nine each of food jars and beverage bottles, that consistently got great reviews online. Our selection included a variety from well-known brands such as Thermos, Stanley and Zojirushi, as well as well-reviewed smaller brands. Most of the beverage thermoses held 1 to 1.5 liters, and the food thermoses held 13 to 18 ounces. As the products started arriving, we read labels and manuals to see what each promised in terms of temperature retention, and measured them to see if they'd fit in lunchboxes and kitchen cabinets. Then we put them through a series of tests and evaluations, using a ThermaPen One instant-read digital thermometer for the most accurate temperature measurements.

Heat Retention Test: To see how well each thermos retained heat, we filled beverage thermoses with 20 ounces of freshly boiled water and food thermoses with 10 ounces of hot tomato soup. We measured the initial temperature, then screwed the caps on tightly. Temperature readings were taken and recorded after one, three and six hours. If the product promised heat retention up to a certain amount of time, such as 15 or 24 hours, we checked the temperature at those times, too. We calculated how much the temperature of the contents decreased over time.

Cold Retention Test: To determine how well each product kept food and drink cold, we filled the beverage thermoses with 20 ounces of ice water to which we added 10 small ice cubes. Food jars were filled with yogurt straight from the refrigerator. Again, temperature checks were performed after one, three and six hours, as well as after any time thresholds promised on the packaging. We calculated how the temperature changed over time and how long ice remained in the beverage bottles.

Leak Test: Nothing's worse than a container that leaks its contents all over your backpack or lunchbox. We filled each container with water and then shook it upside down and rolled it around to see how well the lids kept its contents from leaking or dripping out. These product designers universally did their jobs — not a single one of the products we tested leaked.

Drop Test: Wanting to make sure we choose food and beverage containers that could stand up to some abuse while they're out and about, we filled beverage containers with 20 ounces of water and food containers with eight ounces of water. Then we headed outside and dropped them onto a sidewalk from a height of three feet (about waist height). We checked for dents and scuffs, and to see if the drop caused any leaks.

Overall Performance: We assessed how easy lids were to unscrew, if pour spouts were effective in pouring liquids into a cup, and how easy it was to spoon food from the food jars. We noted any performance or usage flaws.

Finally, we checked whether the containers were dishwasher-safe, and how easy they were to wash by hand, assessing whether the mouth was wide enough for a hand to fit inside or if a bottle brush was needed, and whether lids had lots of parts to lose or if there were deep crevices where food could collect.

What to Consider When Buying a Thermos

Use: Determine whether you will most likely be storing and transporting food or beverages, and whether you'll be eating or drinking directly out of the vessel. Some bottles have a top designed for sipping, while others have lids that convert into cups. Some food containers also have lids that double as bowls.

Capacity: Thermoses come in a range of sizes. The smaller sizes are ideal for lunch or a drink for one, while larger ones can accommodate multiple servings of food or drink.

Features: You might like the idea of an insulated outer lid that doubles as a cup, or a folding spoon that nests inside the lid. Some containers come with carrying handles or even a bag with a strap that makes for easy transport.

Cleaning and Storage: Some of the food thermoses we tested had lids with deep crevices that could collect food residue, making them difficult to clean. Consider whether this would be an issue for you, or if you'd prefer a dishwasher-safe product. For beverage thermoses, we also found that some were simply too tall to store upright or on their side in a cabinet, which could make storage a challenge while not in use. Any beverage thermos measuring less than 13 inches in height will be easier to store.

Frequently Asked Questions

What's the difference between a tumbler and a thermos?

A beverage tumbler is designed to be easy to drink from directly. It likely has an opening for a straw, or a lid with an opening for sipping, but it won't have the same superior temperature-retention properties of a thermos. Many of the beverage thermoses we tested, meanwhile, are designed to store beverages and dispense them into a mug or other drinking vessel, rather than for direct drinking use.

How do thermoses work to keep contents hot or cold?

Thermal containers have a double-walled construction and vacuum insulation. To understand how this technology works, we asked Dr. Taylor Wallace of the Think Healthy Group. "A thermos slows all three ways heat moves — conduction, convection and radiation, with two walls and a near-vacuum between them, plus reflective inner surfaces and a tight lid to cut radiation and air exchange," he says. "With fewer paths for heat to flow, hot things stay hot and cold things stay cold."

How long do thermoses keep food or drinks hot or cold?

The most effective thermal containers in our test kept food and drinks at safe temperatures for as long as six hours. While some brands claim they can keep beverages hot or cold for as long as 24 hours, we found that while they did perform well keeping beverages cold, they weren't as effective in keeping beverages hotter than a tepid temperature.

Can I put carbonated drinks in a thermos?

It is not recommended to put a carbonated drink in a thermos bottle. The carbon dioxide can cause pressure to build up, making the lid difficult to open, or even causing the container to burst.

How can I improve the effectiveness of my thermal container?

Priming the bottle or food jar with hot or cold water can increase the performance of a thermos. For cold foods or drinks, fill the container with ice water for about five minutes, then dump the ice water out and fill it with the preferred contents. For hot foods or drinks, fill the container with boiling water, let it sit for about five minutes, then pour out the hot water and fill with the preferred contents.

Other Thermoses We Tested

Many of the thermoses we tested did a serviceable job keeping their contents hot or cold, making it difficult to choose.

The Thermos The Rock Insulated Bottle was a close runner-up to our cold beverage pick; water only increased in temperature by three degrees, and its rugged design and almost comically oversized carrying handle made it well-suited for outdoor adventures (though not so great for storage).

The Stanley Classic Legendary Insulated Food Jar kept food out of the danger zone for six hours, but didn't live up to its 15-hour promise. With a 24-ounce capacity, it would be great for multiple servings but not so convenient for lunchboxes or daily use.

One surprise was the cult-favorite Yeti Rambler 36-Ounce Bottle. Although we liked that it had a drinking spout, a feature that none of the other bottles had, and it kept cold water at a temperature for six hours, we were surprised when it performed dismally in our hot test, with boiled water cooling by 74 degrees over six hours.

Why You Should Trust Our Tester

A graduate of the Institute of Culinary Education in New York City, Jessica Harlan has been a cooking equipment reviewer and recipe developer for more than 20 years. She's tested everything from peelers to the viral Ninja Creami ice cream makers. She has written nine cookbooks.

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