Are thermos flasks all they’re cracked up to be?
10.8.2018
Translation: Eva Francis
Pictures: Ramon Schneider
The sun is blazing in the sky, luring lazybones into swimming pools and the more adventurous out hiking. What unites them is their thermos flasks – whether it’s keeping their diluted drinks cool or their tea warm. But how well do they work? I tested out eight popular models to find out.
A vanilla ice cream shortage threatens and the mountains are chock-a-block with walking shoes. The sun is showing its best side. If you need a cool drink after a sweaty climb up the mountain or after three hours sunbathing in sweltering heat, the trusty thermos flask is your best friend. It’s also a must-have if you hanker after a steaming hot cup of tea on refreshing summer mornings before work or when the air con is up too high in the office.
That’s why I thought it was high time I put our customers’ favourite brands to the test. And now I’m armed with answers to all your questions, including how long the flasks keep drinks hot or cool, how heavy they are and whether they’re leak-proof.
Test conditions
Here’s how I measured the temperature, you’ll see in all the tables below. I took the first measurement straight after filling up the flasks. Then I took the temperature every hour for eight hours. The last reading was taken the next day, in other words 24 hours after the first. I obviously carried out the same process for hot water and cold water for each flask.
The leak-proof measure also came into the equation. To test that out I filled each thermos with water, shook it vigorously and left it a few minutes upside down (and on its side). I then gave the flask a rating depending if or how much water came out. As a general rule, the more points a flask has, the better it is. That means the higher the rating, the more it’s leak-proof, insulated, lighter and cheaper. The most a flask can score in each category is 5.
For each test, I used the 0.6 litre model to get the most easily comparable results. When quoting prices, I didn’t take into account any promotions and instead listed the standard Galaxus price. While prices were accurate on the date of writing (6 August 2018), they may have changed by the time you read this.
24 Bottles Vivienne Westwood thermos
This stunning thermos flask is the most expensive model we tested, which wasn’t a big surprise given the pot of gold vibes. This Vivienne Westwood design stands for climate revolution and aims to raise awareness of climate change. If this is too flashy for you, there are more basic models available in the range.
What impressed me about this flask was how light it is. It comes in at a mere 312 grammes. As for the lid, the insulation is pretty poor, meaning it gets warm quickly when you’ve got hot liquid inside. That really shouldn’t happen with thermos flasks.
- Keeps stuff cool: ❄️
- Keeps stuff hot: 🔥🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨💨💨💨💨
- Price: 💰
Chilly's Purple
Chilly's makes thermos flasks for the lower price segment. In fact, it’s the cheapest flask I tested. While this one may look plain and simple, there are other colours and patterns available including ones covered in avocados and flowers. In terms of weight, the flask does come in at the upper end of the scale. At 414 grammes, it’s one of the heaviest flasks I tested.
- Keeps stuff cool: ❄️❄️
- Keeps stuff hot: 🔥🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨💨
- Price: 💰💰💰💰💰
Emsa Large Black Travel Mug
Strictly speaking, the Emsa insulated travel mug isn’t a thermos flask but it does accommodate the same amount of liquid and can be used as an insulated container. The rubber grip sleeve comes in different colours. But at a whopping 444 grammes, this mug is the heaviest thing we tested. Even in terms of price, it’s sitting at the top end of the scale.
- Keeps stuff cool: ❄️❄️
- Keeps stuff hot: 🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨
- Price: 💰
Camelbak Forge
This thermos flask was made specially for outdoors enthusiasts. Camelback’s offering may not look as stylish but it is more practical. Every aspect of design has been carefully thought out, from the easy clean design to the drinking system. This flask comes in various different colours and comparatively speaking, the 348 grammes don’t take up much weight in your bag. In terms of cost, this thermos is sitting pretty in the lower price bracket.
- Keeps stuff cool: ❄️❄️❄️
- Keeps stuff hot: 🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨💨💨💨
- Price: 💰💰💰💰
Sigg Accent
The well-known Swiss thermos manufacturer, Sigg, is going back to its roots with this flask. It features clear, simple design and tried and tested insulation. Don’t like this style? It comes in plenty of other guises. While the Sigg thermos flask might be in the top third when it comes to weight (412 grammes), it is mid-range in terms of price tag.
- Keeps stuff cool: ❄️❄️❄️❄️
- Keeps stuff hot: 🔥🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨💨.
- Price: 💰💰💰💰
Unfortunately, it was only after carrying out the test that I discovered this model isn’t made anymore. The good news is we are stocking the latest version of the flask in the Galaxus shop. I just can’t guarantee if it performs as well as it’s older sibling.
Asobu Le Baton
Le Baton from Asobu sets a new benchmark in design. This stylish flask sits comfortably in the mid-range, with its svelte proportions (400 grammes) dropping the thermos into the lower weight range and the price pushing it towards the higher bracket. Le Baton comes in three different lid colours. Similar to the Vivienne Westwood model, this flask can be a struggle to open when it has warm liquid in it because the lid gets very hot.
- Keeps stuff cool: ❄️❄️❄️❄️
- Keeps stuff hot: 🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨💨💨
- Price: 💰💰
FLSK flask
The FLSK thermos keeps the traditional flask shape and comes in a handful of colours. It is slightly more expensive than the Camelback and Sigg models and at 440 grammes, it does weigh more than the other flasks. But the points it loses in weight it makes up for in its leak-proof qualities – and its ability to keep your stuff hot or cool.
- Keeps stuff cool: ❄️❄️❄️❄️❄️
- Keeps stuff hot: 🔥🔥🔥🔥🔥
- Leak-proof: 💧💧💧💧💧
- Weight: 💨
- Price: 💰💰💰
ZOKU stainless steel flask
ZOKU has delivered a mid-range priced thermos with this stainless steel creation. At 400 grammes, this insulated flask is also slap-bang in the middle when it comes to weight. Instead, ZOKU has focused on honing its unique vacuum insulation technology.
- Keeps stuff cool: ❄️❄️❄️❄️
- Keeps stuff hot: 🔥🔥🔥
- Leak-proof: 💧
- Weight: 💨💨💨
- Price: 💰💰💰
Results in table form
Results when I put the flasks to the test with cold tap water:
| Flaschenmodell | Ausgangstemp. | Nach 1h | Nach 2h | Nach 3h | Nach 4h | Nach 5h | Nach 6h | Nach 7h | Nach 8h | Nach 24h |
|---|---|---|---|---|---|---|---|---|---|---|
| 24 Bottles | 20.9 | 21.2 | 21.6 | 21.9 | 22.4 | 22.9 | 23.4 | 23.8 | 24.2 | 27.0 |
| Chilly's | 20.5 | 20.9 | 21.2 | 21.4 | 21.6 | 21.9 | 22.2 | 22.5 | 22.8 | 25.6 |
| Emsa | 20.9 | 21.2 | 21.5 | 21.7 | 21.9 | 22.3 | 22.7 | 23.2 | 23.4 | 26.3 |
| Camelbak | 20.6 | 20.7 | 20.8 | 21.2 | 21.5 | 22..0 | 22.2 | 22.6 | 23.0 | 25.4 |
| Sigg | 20.7 | 20.9 | 21.0 | 21.2 | 21.4 | 21.6 | 21.8 | 22.0 | 22.2 | 23.9 |
| Asobu | 20.5 | 20.6 | 20.7 | 20.8 | 21.0 | 21.2 | 21.4 | 21.6 | 21.9 | 23.6 |
| FLSK | 20.7 | 20.8 | 20.9 | 21.0 | 21.1 | 21.2 | 21.3 | 21.4 | 21.5 | 23.1 |
| ZOKU | 20.5 | 20.7 | 20.9 | 21.0 | 21.2 | 21.4 | 21.5 | 21.8 | 22.0 | 23.9 |
And here are the results when I tried with hot water:
| Flaschenmodell | Ausgangstemp. | Nach 1h | Nach 2h | Nach 3h | Nach 4h | Nach 5h | Nach 6h | Nach 7h | Nach 8h | Nach 24h |
|---|---|---|---|---|---|---|---|---|---|---|
| 24 Bottles | 93.1 | 88.3 | 83.1 | 78.2 | 74.1 | 70.0 | 66.7 | 64.1 | 61.8 | 40.0 |
| Chilly's | 93.3 | 88.4 | 83.4 | 79.1 | 75.1 | 71.0 | 67.6 | 65.1 | 62.3 | 40.3 |
| Emsa | 93.7 | 87.3 | 81.8 | 76.7 | 71.9 | 67.3 | 63.7 | 61.3 | 58.5 | 38.3 |
| Camelbak | 93.3 | 83.9 | 75.4 | 68.4 | 62.8 | 57.6 | 53.9 | 51.4 | 48.9 | 31.5 |
| Sigg | 93.4 | 89.3 | 84.9 | 80.8 | 77.5 | 73.6 | 69.8 | 67.4 | 65.3 | 43.9 |
| Asobu | 93.9 | 87.7 | 81.3 | 75.6 | 70.5 | 66.7 | 62.5 | 59.8 | 57.4 | 36.8 |
| FLSK | 93.1 | 90.1 | 86.8 | 83.6 | 80.8 | 77.6 | 75.2 | 73.1 | 71.2 | 50.9 |
| ZOKU | 93.7 | 88.1 | 82.8 | 78.0 | 73.5 | 69.5 | 66.3 | 63.7 | 61.2 | 38.9 |
Verdict
Surprisingly, the only thermos that didn’t stay leak-proof from the start was the ZOKU stainless steel flask. When I turned it upside down, lay it on its side and shook it, water came out. When I opened it and closed it again, a lot less water escaped.
The third time I tried opening and reclosing it, the flask stayed leak-proof. But that’s neither here nor there. It should have been watertight from the get-go. No one wants the contents of their bag getting wet.
When it came to keeping the contents cool, the FLSK flask impressed me the most. Eight hours later, the water was only 0.8℃ warmer. Even after a whole day in 30℃ ambient temperature, the liquid was only 2.4℃ warmer.
The flask that fared worst for keeping water cool was the 24 Bottles Vivienne Westwood thermos. After eight hours, the water temperature had increased by 3.3℃ and after 24 hours by 6.1℃.
In terms of keeping the water hot, the FLSK flask comes out on top again. It was the only flask to keep the water above 80℃ after four hours. Even after eight hours, the water temperature only dropped by just over 20 degrees. The straggler in this test was Camelbak’s Forge, which had lost almost half the water heat by the end.
And so it’s no surprise that my clear favourite and winner of this test is the FLSK flask. Its excellent insulation and the decent price tag make up for it carrying more weight. This thermos flask definitely comes recommended. The Sigg, Chilly's and Camelbak products I tested were also impressive.
Meanwhile, the clear loser in this test is Esma’s Large Travel Mug in black. The high price, weight and average insulation just aren’t in its favour.
Header image: The eight objects of desire: I tested thermos flasks of various brands.
Raphael Knecht
Senior Editor
raphael.knecht@digitecgalaxus.chWhen I'm not stuffing my face with sweets, you'll catch me running around in the gym hall. I’m a passionate floorball player and coach. On rainy days, I tinker with my homebuilt PCs, robots or other gadgets. Music is always my trusted companion. I also enjoy tackling hilly terrain on my road bike and criss-crossing the country on my cross-country skis.
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