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Cleaning is often done by hand: not all thermo mugs are dishwasher safe

Photo: Jonas Mielke / DER SPIEGEL

If you travel a lot, you need patience and a good thermos mug. Because a hot coffee or tea makes it easier when the train is a long time coming or you are stuck in a traffic jam with your car again. The paper cups handed out by cafés and bakeries for to-go customers, on the other hand, are rarely a source of joy.

Keeping warm, staying tight: these are the basic requirements for a thermos mug. The perfect temperature of a coffee or tea may be just as much a matter of taste as the perfect design. But no one wants to put a container that is potentially leaking in their pocket.

The good news is that the six thermo mugs we tested all held tight – excellent. As long as you close them correctly, you can shake and shake them as much as you want, nothing drips and nothing leaks out. But it is not possible to tell at first glance whether they have actually been closed correctly.

Here's how we tested

Of course, the decisive factor is whether the cups really keep the drinks you pour into them warm. For our test, we measured with an infrared thermal imaging camera, not scientifically exact, but as meticulous as possible. We boiled water, poured it into the cups at a temperature of about 77 degrees, screwed the lids shut – and measured at 60-minute intervals how hot the water still was.

However, because thermo mugs are not only worn indoors in everyday life, we have created two series of measurements: one at room temperature, one with the containers in the refrigerator, at about seven degrees Celsius.

In almost all of the cups we tested, the water was still more than 50 degrees Celsius after four hours – at room temperature. In the refrigerator, only three of the six containers manage to do this after four hours. After five hours in the refrigerator, the wheat was separated from the chaff: While some models still kept the water warm at 45 degrees, others had already dropped the temperature to 40 degrees.

Heat is relative

Which temperature is perceived as warm or lukewarm differs from person to person. WMF promises that the product will keep you warm for eight hours. Stanley vouches that the contents will remain hot for five hours. What the companies call warm or hot, however, is not underpinned by concrete temperature information. The manufacturer's information on heat storage should therefore often be taken with a grain of salt.

A not entirely unimportant difference is how easy the different thermo mugs are to clean after use and how well or poorly they are actually suitable as drinking vessels. Some cups in the test are dishwasher safe, others are not. The Stanley company warns that their product can age faster if it is machine-washed.

We have compiled everything you need to know about the six models we tested below.

Stanley Classic Trigger-Action Travel Mug

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Photo: Jonas Mielke / DER SPIEGEL

A fall from a distance of one kilometer or a category five hurricane: that's what a Stanley cup is supposed to survive, if you believe the manufacturer's label. We didn't try that.

Instead, we tested it in everyday life, and it does well there. The compact and robustly processed stainless steel cup holds up to 0.36 litres of liquid. It should fit in most cup holders on the bike or in the car. In our temperature test, it keeps drinks a few degrees Celsius warmer than others: after seven hours, water has cooled down from 77 degrees to 48 degrees at room temperature.

The locking mechanism can be operated with one hand, you press a button to drink, which is probably where the name of this cup comes from. In addition, it can be cleaned in the dishwasher and the lid is easy to disassemble, which makes cleaning easier.

What you like: Compact and robustly processed. In our test, the cup keeps drinks up to seven degrees Celsius warmer than others after seven hours.

The less: The cap is easy to use, but you have to find the right position for drinking. When driving, this can be distracting.

WMF Impulses

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Photo: Jonas Mielke / DER SPIEGEL

As expected, the Impulse thermo mug from WMF exudes more design charm than camping flair. The stainless steel vessel can hold 0.35 litres of coffee, tea or other beverages. According to the WMF, the cup should keep them warm for up to eight hours. In our test, the 77-degree hot water was still 47 degrees Celsius after seven hours. Not significantly better than other models, but not worse either.

Even if you hold it with only one hand, it is easy to drink from the cup: If you press on the lid, it lowers a little and you can start drinking all around. Unfortunately, it is hardly possible to tell whether the mechanism is open or closed. This led to a small breakdown and spilled coffee in the test.

According to the manufacturer, the WMF thermo mug is not suitable for dishwashers.

What you like: In addition to the design, I particularly like the fact that you don't have to aim at a specific spot on the lid when drinking, but can apply it almost blindly at any point.

The less: In everyday life, it is more practical to simply put the mug in the dishwasher in the evening. It would be easier to tell whether the shutter is open or closed.

Contigo West Loop

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Photo: Jonas Mielke / DER SPIEGEL

If you prefer to take a little more coffee with you on the way, you can choose the Contigo West Loop. It has a capacity of 0.47 litres, but is not significantly larger than the other cups in the test field. In the temperature test, it delivered the worst readings. At room temperature, the water filled with 77 degrees Celsius was only 41 degrees Celsius seven hours later.

The drinking mechanism works similarly to that of the Stanley model, but can be additionally secured: in addition to the button for drinking, there is another button that locks the mechanism against accidental opening, so that no coffee escapes by accident. It's a good feeling when you stow the mug in your backpack, where it rocks back and forth.

The stainless steel cup is not dishwasher safe, only the lid is allowed in the machine according to the manufacturer. On the other hand, it can't be taken apart, but you can still get into all corners relatively well.

What you like: Relatively compact design, but still large volume.

The less: Drinks lose temperature a little faster in this thermo mug than in the other models tested.

Emsa Travel Mug Waves

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Photo: Jonas Mielke / DER SPIEGEL

The only stainless steel cup in the test that has a silicone sleeve. This makes it feel a bit more slip-resistant, but looks more like a design element in comparison. The Emsa model lands in the solid midfield in our test when it comes to keeping warm.

The drinking mechanism works in a similar way to that of the WMF Impulse: after pressing the button in the middle of the lid, you can attach the cup, no matter where it is. Although it is tricky to open the Emsa with one hand, you can easily see whether the drinking opening is open or closed. Practical: It is also dishwasher safe.

What you like: The Emsa Travel Mug Waves has a nice grip and makes it easy to use, because you are not limited to a specific place in the lid when drinking.

The less: This model is almost impossible to use with one hand

Elasto Personalised Stainless Steel Travel Mug

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Photo: Jonas Mielke / DER SPIEGEL

The stainless steel model from the promotional gift manufacturer Elasto looks less solidly made than the products of the competition, especially on the lid. Compared to the other cups in the test, it feels less comfortable when drinking. You have to put your head far back so as not to bump your nose against the lid (at least with the nose with which the test was carried out).

The Elasto product has a capacity of a whopping 0.45 litres, but scores rather mediocre in our temperature test: After four hours in the fridge, water in it is only 43 degrees Celsius – ten degrees Celsius colder than in other models. Nevertheless, it fulfils its purpose on short commutes.

In addition, the Elasto can be individually labeled. Our test model was adorned with the song quote »Shine bright like a diamond«. Sure, that's a matter of taste, but such decorations are otherwise not possible with any of the other cups in our test.

What you like: Creative individualists can let off steam with the labeling of their cup.

The less: Loses heat faster than the other thermo mugs in the test.

Primus Trailbreak Vacuum Bottle

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Photo: Jonas Mielke / DER SPIEGEL

The Primus model is more of a thermos than a thermos mug. This means that if you want to take 0.5 liters of hot coffee with you, you will need more space in your backpack or car. For some cup holders, this cup may be too big.

Nevertheless, the Primus vessel in our test stores heat best. After seven hours at room temperature, it is the only model in which the water is more than 50 degrees Celsius, exactly 52 degrees Celsius.

In addition, the Primus is supplied with two lid attachments. One of them is meant for drinking, the other serves as a classic screw cap if you prefer to drink from the cup that is also included.

What you like: The model from Primus keeps hot liquids warm best in our test and has the largest capacity.

The less: In everyday life, the size can also be a disadvantage.

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