You are using an older browser version. Please use a supported version for the best MSN experience.

The Best Insulated Thermoses, Tested

Popular Mechanics Logo By Roy Berendson, James Lynch, Adrienne Donica of Popular Mechanics | Slide 1 of 9: Call it a thermos, travel mug, or insulated water bottle, there’s no substitute for one of these multipurpose containers when you want to keep your drinks hot or cold. The best ones do so for longer and have other features, such as wide-mouth openings that make them easier to fill, clean, and add ice. They’re durable, less prone to leaking, and lighter than those that came before. We put a wide crop through the testing wringer to determine which tick those boxes.How Does a Thermos Work?Most rely on double-wall or even triple-wall construction, and the space between each wall is vacuum-sealed. Because it’s devoid of air, this gap slows the transfer of heat. Simply stated: The less air, the less heat flow. Insulated windows work the same way. You have two or three panes of glass joined in one sealed assembly, and each pane of glass is separated not by air but an inert gas that’s a poor conductor of heat. Scottish physicist and chemist James Dewar noticed this effect and, in 1892, invented the vacuum flask, a container with an inside and outside wall separated by a vacuum. Dewar’s flask was the forerunner of today’s thermos. The gap between the container’s inside and outside walls doesn’t have to be wide, it just needs to be absent of air to be effective.Related: The Best Hydro Flasks | Quench Your Thirst Anywhere With These Great Water BottlesThermos Care and UseIt’s simple to maintain a thermos. Try not to drop it or bang it around, which may break its vacuum seal. Keep it clean, and make sure to remove and give the lid’s gasket a good scrub every once in a while. Most thermoses aren’t dishwasher-safe. Sometimes their lids are, but the bottle may not be rated to withstand the thermal cycle of a dishwasher. Three of the bottles on this list are, but when in doubt, wash by hand. For the bottles with a narrow mouth, you might find a bottle brush helpful.While we won’t do a deep dive into thermodynamics here, suffice it to say that a wide range of factors can influence the temperature of the liquid in a thermos. To keep the contents hot or cold, stash the thermos in a place that’s hot or cold. Say you want your coffee to stay hot on a winter day, keep the thermos in a pack surrounded by something that will insulate it. Or leave it in your car, especially if there’s sun coming through the windows. If the contents should stay cold, put the thermos in the shade or a cooler. Be mindful of where you set the thermos down. For example, placing it on hot asphalt during a picnic will increase the rate of heat flow from the pavement to the thermos. Your ice-cold water will warm up more quickly. Yes, a thermos with an insulated lid and a vacuum seal at its base resists heat loss or gain more than other designs. But regardless of the construction, with a little common sense you’ll reduce the rate at which the thermos reaches temperature equilibrium with its surroundings.How We TestedWe put 30 thermoses to the test to see which will keep your hot liquid hot the longest and which will protect that nice chilled drink from heating up.The hot test: We filled each thermos to the very top (as high as we could without spilling) with 190-degree Fahrenheit water. We then closed the lids and let them sit for 24 hours. Before opening, we shook them to distribute any hot water that may have risen to the top, then tested each with the same infrared thermometer that measured the starting temperature. We then emptied the bottles and let them sit for three hours so that all parts of the bottles would return to room temperature, without retaining any heat from our earlier tests, before continuing to part two.The cold test: We filled each bottle to the very brim with chilled water, all thermometer-confirmed at a cool 46 degrees. Again, we sealed up the bottles and let them sit for 24 hours. The next day we shook them, opened each, and checked the temperature.Using these measurements, we calculated the heat loss for our hot test and heat gain for our cold test. For both, a smaller number is preferred. We also used these bottles as you will, seeing how easy they are to drink from, close, open, toss into a bag, and clean. We wanted to see how well they’d fit into our life to know how well they’ll fit into yours.

Call it a thermos, travel mug, or insulated water bottle, there’s no substitute for one of these multipurpose containers when you want to keep your drinks hot or cold. The best ones do so for longer and have other features, such as wide-mouth openings that make them easier to fill, clean, and add ice. They’re durable, less prone to leaking, and lighter than those that came before. We put a wide crop through the testing wringer to determine which tick those boxes.

How Does a Thermos Work?

Most rely on double-wall or even triple-wall construction, and the space between each wall is vacuum-sealed. Because it’s devoid of air, this gap slows the transfer of heat. Simply stated: The less air, the less heat flow. Insulated windows work the same way. You have two or three panes of glass joined in one sealed assembly, and each pane of glass is separated not by air but an inert gas that’s a poor conductor of heat. Scottish physicist and chemist James Dewar noticed this effect and, in 1892, invented the vacuum flask, a container with an inside and outside wall separated by a vacuum. Dewar’s flask was the forerunner of today’s thermos. The gap between the container’s inside and outside walls doesn’t have to be wide, it just needs to be absent of air to be effective.

Related: The Best Hydro Flasks | Quench Your Thirst Anywhere With These Great Water Bottles

Thermos Care and Use

It’s simple to maintain a thermos. Try not to drop it or bang it around, which may break its vacuum seal. Keep it clean, and make sure to remove and give the lid’s gasket a good scrub every once in a while. Most thermoses aren’t dishwasher-safe. Sometimes their lids are, but the bottle may not be rated to withstand the thermal cycle of a dishwasher. Three of the bottles on this list are, but when in doubt, wash by hand. For the bottles with a narrow mouth, you might find a bottle brush helpful.

While we won’t do a deep dive into thermodynamics here, suffice it to say that a wide range of factors can influence the temperature of the liquid in a thermos. To keep the contents hot or cold, stash the thermos in a place that’s hot or cold. Say you want your coffee to stay hot on a winter day, keep the thermos in a pack surrounded by something that will insulate it. Or leave it in your car, especially if there’s sun coming through the windows. If the contents should stay cold, put the thermos in the shade or a cooler. Be mindful of where you set the thermos down. For example, placing it on hot asphalt during a picnic will increase the rate of heat flow from the pavement to the thermos. Your ice-cold water will warm up more quickly. Yes, a thermos with an insulated lid and a vacuum seal at its base resists heat loss or gain more than other designs. But regardless of the construction, with a little common sense you’ll reduce the rate at which the thermos reaches temperature equilibrium with its surroundings.

How We Tested

We put 30 thermoses to the test to see which will keep your hot liquid hot the longest and which will protect that nice chilled drink from heating up.

The hot test: We filled each thermos to the very top (as high as we could without spilling) with 190-degree Fahrenheit water. We then closed the lids and let them sit for 24 hours. Before opening, we shook them to distribute any hot water that may have risen to the top, then tested each with the same infrared thermometer that measured the starting temperature. We then emptied the bottles and let them sit for three hours so that all parts of the bottles would return to room temperature, without retaining any heat from our earlier tests, before continuing to part two.

The cold test: We filled each bottle to the very brim with chilled water, all thermometer-confirmed at a cool 46 degrees. Again, we sealed up the bottles and let them sit for 24 hours. The next day we shook them, opened each, and checked the temperature.

Using these measurements, we calculated the heat loss for our hot test and heat gain for our cold test. For both, a smaller number is preferred. We also used these bottles as you will, seeing how easy they are to drink from, close, open, toss into a bag, and clean. We wanted to see how well they’d fit into our life to know how well they’ll fit into yours.

© Trevor Raab

More from Popular Mechanics

Popular Mechanics
Popular Mechanics
image beaconimage beaconimage beacon