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Best Thermoses: Insulated Flasks for Every Need

We spent over 100 hours testing thermoses, insulated flasks and food vacuum jars, and the best is the Stanley Classic. This well-designed and durable thermos keeps liquids hot or cold for 24 hours with minimal temperature change. The insulated walls keep the outside of this thermos from heating up or cooling down and prevents condensation from building. The Stanley Classic holds 35 ounces, which is perfect for sharing a drink, or staying hydrated during a long hike or outing. 

Best Overall

Stanley Classic

Stanley Classic

Holds 35 ounces
Good for outdoor enthusiasts
Keeps drinks hot or cold for 24 hours
Heavy and bulky
Not dishwasher safe
Doesn't fit in car cup holders

For five days the Stanley Classic kept ice cubes cold with very little melting, and in both our hot and cold tests, this thermos easily kept liquids near their original temperatures for 24 hours

In our tests of the best thermoses, the Stanley Classic only warmed up by 15 degrees during the cold tests, and it cooled down only 8 degrees during the heat retention tests. This thermos is bulky because of all the insulation needed to keep inside temperatures consistent. And it holds 35 ounces, so it can get pretty heavy. But the two leakproof caps keep the Stanley Classic from spilling if it’s bumped and bounced around in a backpack. This is a good thermos for taking along on picnics or fishing trips, especially if you have more than one person who needs to stay hydrated. And the outer cap doubles as a cup so you don’t have to drink straight from the thermos. The Stanley thermos doesn’t fit in a dishwasher because of its sheer size (it’s handwash only anyway) and it’s too big to fit in car cup holders, so it isn’t an easy grab and go option.

Best Value

Hydro Flask Standard Mouth

Hydro Flask Standard Mouth

Includes a lifetime warranty
Several sizes to choose from
Prevents condensation
Loses heat quickly
Isn’t dishwasher safe
Doesn’t fit in stroller cup holders

The Hydro Flask Standard Mouth insulated thermos is the best value in large part because of the lifetime warranty that comes with it. But it is also a good quality thermos that doesn’t leak when shaken or bounced in a backpack.

This vacuum thermos fits nicely in standard car cup holders and holds 18 ounces of your favorite drink. It keeps coffee hot for 12 hours, though it does lose heat quickly, about 86 percent after two hours. During our tests, the average thermos filled with hot liquid cooled by 76 degrees after 12 hours (from 188 degrees to 117 degrees F), even when we prefilled the thermos to heat the inside before finally filling it. So, this coffee thermos works best if you’re planning on enjoying your drink within a couple hours of pouring it. The insulated walls keep the outside of the thermos from changing temperature, so you can always comfortably hold your drink. It also doesn’t collect condensation. While the Hydro Flask thermos is BPA free, it isn’t dishwasher safe, so you should wash the entire container, including the lid, by hand.

Best Food Thermos

Zojirushi Stainless Steel Food Jar

Zojirushi Stainless Steel Food Jar

Wide mouth for easy use
Retains heat well
Leak-proof seal
Not suitable for dairy products
May retain odors
Handwash only

The Zojirushi food jar’s wide-neck design lets you ladle hot soup, chili or pasta into the container without making a mess, and it’s equally easy to spoon out the food without contorting your hand in awkward positions. Plus, it keeps food really hot, only cooling down by 38 degrees in the six hours we tested it.

This Zojirushi holds 25 ounces, more than double the amount of other food thermoses we tested, so it’s a good option for middle or high schoolers who need a bigger lunch at school, or for on-the-go adults who need a healthier option than fast food. This food jar keeps cold foods chilled for six hours, too, though Zojirushi does advise against toting raw or cold dairy products in this container. You can place the Stainless Steel Food Jar directly into your child’s backpack because even with all the shaking and bumping, the threaded gasket seal lid stays snuggly sealed and doesn’t leak. As with most thermoses, this one isn’t dishwasher safe, and there have been reports that it can retain odors from extra smelly foods.

Best Commuter Thermos

Contigo West Loop

Contigo West Loop

Fits in most car cup holders
Isn’t designed for food

The Contigo West Loop thermos is a great choice for commuters because it holds 16 ounces of coffee, keeps it hot for five hours and fits snuggly in most car cup holders. The leak-proof lid has an easy-sip spout that can be unlocked with one hand then re-secured after enjoying a sip.

Plus, you can control how fast the liquid pours out so you’re not surprised with a rush of hot coffee. If you find 16 ounces isn’t enough, Contigo does offer 20-ounce and 24-ounce options.
The insulated walls keep the heat inside while keeping the outside walls cool to the touch. Or, if you prefer an iced latte, the thermos will keep it cold for 12 hours on the inside without freezing your fingers on the outside. The Contigo thermos isn’t built to handle foods, so its restricted to drinks only, but its unique lid is dishwasher safe if placed on the top rack. The body of this thermos should be handwashed.

Why Trust Us

Top Ten Reviews has been researching and testing home products since 2010, and for the past three years we have invested several hundred hours examining thermoses. We looked at a wide variety of thermoses and insulated food containers and spoke with moms, commuters and outdoor enthusiasts who tend to use these items frequently to learn about their experiences with different types of thermoses and the brands they purchase.

For example, Richelle Kimbal, a mother of four, bought an insulated food jar to send hot lunch to school with her second grader during the cold winter months. Kimbal was so impressed with the quality, value and ease of using it that she purchased a second one when another child started all-day school. We used this feedback while examining different characteristics of insulated food jars, such as wide mouths, durability, spill-proofing and ease of washing them. We also considered cost since that is an important determining factor for many people.

Another consumer we spoke with is Anna Burleson, who totes an insulated thermos to the office in the morning with several ounces of coffee. Burleson pointed out that during her commute it’s important that the flow of coffee from the pour spout is consistent to avoid burns, and equally important is to control the speed of the flow. Also, being able to unlock and open the flask with one hand is necessary. With this information we looked closely at pour spouts, cap locks and ease of opening and closing them, plus which thermoses fit into standard car cup holders.

How We Tested

We conducted multiple temperature tests to see if the manufacturer’s claim of how long a thermos keeps food or liquid hot or cold was accurate. After filling each thermos with a consistent hot or cold temperature measured water, we waited for the claimed hours to go by. We then opened the thermoses and remeasured the water to learn how much heat was lost, or how warm cold water became as it sat untouched.

Hot Water Tests
According to a study published by the US National Library of Medicine National Institute of Health, researchers at The University for Texas at Tyler found coffee, tea and other hot beverages are typically served between 160 and 185 degrees F. For heat tests, we added water heated with a sous vide machine to 200 degrees F. When it was transferred to the thermoses, the water cooled to 188 degrees F. We performed multiple tests, with some testers filling thermoses at room temperature and others pre-filling the thermoses with hot water to heat the inside first. We didn’t see much difference in how quickly the water cooled between the pre-filled and non-pre-filled thermoses. On average hot water cooled by 55 degrees after sitting between six and 12 hours, with another 15-degree cooldown at the 12-hour mark. 

We wanted to learn the average heat loss for each thermos, so we filled each pre-filled thermos with 188-degree F hot water then remeasured after only two hours. The best insulated thermoses retained over 90 percent of the water’s heat, though several dipped down to 80 percent heat retention. Only one thermos retained less than 70 percent of its water’s heat after two hours.

Cold Water Tests
As with the heat tests, we started by filling each thermos with water that had been chilled to 33 degrees F, which is 1 degree warmer than water’s freezing point. We noted how long each thermos claimed it could keep water cold, and we measured the water temperature once that time had elapsed. On average the water warmed by 23 degrees to a temperature of about 58 degrees F, still 15 degrees colder than room temperature.

Food Jar Tests
For the three food jars we tested, we wanted to learn how hot the food stayed after sitting in the thermos for six hours, which is the amount of time manufacturers claim their jars keep food warm. We heated soups, chowders and Top Ramen to 187 degrees F, which is 27 degrees hotter than food should be heated to kill any foodborne bacteria. There was a decent difference in heat loss between the food jars with a range of 33 to 66 degrees of cooldown. This still kept foods at a decent, enjoyable temperature after six hours of sitting. 

Leak-Proof Tests
We subjected each thermos to vigorous shaking, tipping, jostling and bouncing to see how tightly the lids sealed. Even the food jars, filled with hot soup, were turned over and tossed to make sure they wouldn’t open in your child’s backpack. With the exception of one thermos, every one kept a very tight seal. The Asobu Imperial Beverage Cup was the only thermos that leaked…a lot. And unfortunately, the first time we performed a leak-proof test with this product the water was a bit hot and caused some burns on the hands of one of our testers. 

Other Tests
In addition to our temperature retention tests, and our leak-proof observations, we also checked out which thermoses fit well in car cup holders and in stroller cup holders. We learned that stroller cup holders are substantially smaller than those in cars and most thermoses don’t fit well. Even most standard water bottles are too big to fit. Kimbal expressed her frustration with not being able to tote along a hot or cold drink during her morning run with two children strapped into her jogging stroller. Instead she places her thermos in the carrying basket under the stroller but mentioned this is very inconvenient since it requires her to stop and bend down to find her drink when she needs to rehydrate. 

How much does a decent thermos cost?

Because there are so many kinds of thermoses and food jars available, there isn’t a clear-cut answer to how much one costs. However, you can expect to spend between $15 and $20 for a decent thermos that is well insulated, holds a good amount of liquid and includes a leak-proof lid. Most thermoses in this price range also come with a warranty to cover major manufacturing defects.

Things to Look for in a Thermos

Whether you are toting icy water to hydrate you after a long workout or bringing warm baby food with you to keep a hungry child happy, having a quality thermos can make or break your outing. Different thermos models have different characteristics, so you’ll need to choose the one that works best for your situation.

Construction & Insulation
Construction and insulation can profoundly affect temperature retention and durability. There are plastic and pressed tin models on the market, but better- quality thermoses give you a double-walled stainless steel construction. This provides strength, scratch resistance, shatterproofing and corrosion resistance. Stainless steel is also able to withstand the pressure of vacuum insulation. This type of insulation maintains temperature with airless space between the two walls of the thermos. This prevents heat or cold leaching into or out of the interior, which means a flask with good quality vacuum insulation holds heat or cold for longer intervals than one with foam insulation.

The capacity of a thermos dictates how many people can stay hydrated and for how long. With capacities ranging from 4 ounces to 1 gallon, you should choose the size of your flask based on its most likely use. If, for example, you need a thermos for hiking, family picnics or other all-day or overnight activities, you’ll no doubt need one with a substantial capacity. For your own hydration during a workout or a hot drink on the daily commute, a single-serve travel mug or travel tumbler that holds between 4 and 16 ounces probably would work better.

If you're looking for a thermos that's easy to carry while you run or work out, consider one that comes with a carry strap, clips to your belt or has a contoured body for a comfortable grip. For drinks while driving, opt for a slimline travel mug that fits into a vehicle cup holder. When you require a large-capacity flask, look for one with a carry handle, strap or case. For storing in a backpack or lunchbox or to carry over rough terrain, the flask needs to be airtight so it doesn't leak.

ProductPriceOverall RatingTest ResultsConstructionSuggested Manufacturer PriceWarrantyClaimed Hours HotHeat Lost After Claimed Hours (degrees F)Heat Retention After 2 Hours Claimed Hours ColdWarm Up After Claimed Hours (degrees F)Leak-ProofFits In Car Cup HolderFits In Stroller Cup HolderLiquidsFoodsBPA FreeVacuum SealedDouble-walled or InsulatedStainless Steal WallsDishwasher SafeNumber of Fluid OuncesHeight (inches)Width (inches)Weight (ounces)Base Diameter
Stanley ClassicView Deal4.5/554.5$40Lifetime24-659524.+15YesNoNo3514.254.530.44.5
Hydro Flask Standard MouthView Deal4.5/54.54.5$29.95Lifetime12-768624.+29YesYesNo188.42.9112.9
MIRA Lunch Food JarView Deal4.5/555$15.5030 Days5-408410.+20YesYesNo13.553.213.63.2
Thermos SippView Deal4.5/555$24.9930 Days12-549124.+18YesYesYesX169.82.982.9
Zojirushi Food JarView Deal4.5/54.55$28.995 Years6-38916.+36YesNoNo257.2414.14
Contigo West LoopView Deal4/54.55$20.995-578012.+16YesYesNoLid only167.83163.5
Reduce Vacuum Food Jar 12oz, BlueView Deal4/54.55$12.996-6482No ClaimNot TestedYesYesNoLid only125.43.530.43.5
YETI RamblerView Deal3.5/555$39.9924-839224.+22YesYesNoX2610.5430.43.5
Asobu Imperial BeverageView Deal3.5/53.55$19.993-5569No ClaimNot TestedNoYesYesX104.535.93