We have tested the best thermoses on the market in 2019 and name the Thermos King Flask as our Best Choice. This classic model from the company that invented thermoses has very good heat retention, seals tightly and can easily withstand a knock or two. We were also impressed by the Stanley Adventure Vacuum Bottle, a reliable and classic thermos made from stainless steel with a clean design and good build quality. Alternatively the IsoSteel Quickstop is a cheaper thermos with good heat retention capacity for those on a budget.
We carried out the test ourselves and tested all the products as they are intended to be used in reality. We first took the thermoses out into the wilderness, where they were used by two outdoor-loving families. The families were asked to open, pour, drink from, drop and handle the thermoses in all possible ways, with and without gloves and with both small and large hands. We then carried out more controlled testing both indoors and outdoors. In these tests we filled each thermos with boiling water and measured the temperature after 30 minutes and then after 1, 2 and 4 hours respectively. We also stood them upside down to see if they leaked at all. In our assessment we focused on the following areas:
Heat retention capacity: How effectively does the thermos keep its contents hot?
Construction: How impact and shock resistant is the thermos? How well does it prevent leakage? Is it well designed? How heavy is it and how big is the opening you drink from?
Ease of use: How light, neat and stable is the thermos? Can you remove and replace the lid even with damp gloves or weak hands? If the thermos has a snap lid can it be resealed easily? Does it fit into a smaller rucksack? How easy is it to clean? Is it dishwasher safe? How clear are the instructions?
We gave each thermos a score according to its value for money; effectively judging how good each thermos performed in relation to its price tag. We thus had higher expectations for an expensive thermos than for a cheaper one, and vice versa. We counted thermoses costing less than £25 as budget class, and those costing between £25 and £40 as medium class. If they cost more than this, we counted them as premium class.
A classic thermos that you can rely on all day long
Price class: Medium External diameter: 70 mm Diameter opening: 42 mm Height: 250 mm Weight: 360 grams Volume: 470 ml Heat retention capacity: 100 -> 82 °C after 4 hours at room temperature, 100 -> 90 °C after 1 hour at -10 °C
We've chosen the Thermos King Flask as our Best Choice. This thermos is a true classic, made in a factory established in 1929 by the Thermos company after which all thermos flasks are named. The Thermos King Flask, with its attractive retro style and metallic paint, is made from uncrushable stainless steel and managed to withstand both our leak and drop tests with flying colours.
The King Flask maintained high temperatures throughout both our outdoor and indoor testing, whilst the outside of the flask remained cool. The lid of the thermos is easy to use even for children and elderly people and can straightforwardly be removed and replaced even when wearing gloves. However, we felt that the opening could be larger to help with cleaning it. The Thermos King Flask is ideal for someone who wants an attractive thermos that delivers what it promises.
A useful thermos with a timeless design
Price class: Medium External diameter: 70 mm Diameter opening: 43 mm Height: 240 mm Weight: 513 grams Volume: 500 ml Heat retention capacity: 100 -> 81.1 °C after 4 hours at room temperature, 100 -> 88.7 °C after 1 hour at -10 °C
The Stanley Adventure Vacuum Bottle is a substantial stainless-steel thermos with a classic style. While this thermos was invented and has been manufactured since 1913, its design doesn't seem to have aged for the thermos managed to keep liquid warm both during our indoor and outdoor tests. In addition to this it's leak proof, can tolerate being dropped and is straightforward to use even for younger children. The construction is simple with a screw top and a normal thermos mug. The only slight negative detail about this thermos is that the opening is a bit too small, which makes cleaning it somewhat difficult. The Stanley Adventure Vacuum Bottle is without a doubt a stylish, reliable and classic thermos for all outdoor trips.
A trustworthy thermos at a lower price
Price class: Budget External diameter: 75 mm Diameter opening: 31 mm Height: 270 mm Weight: 440 grams Volume: 500 ml Heat retention capacity: 100 -> 81.6 °C after 4 hours at room temperature, 100 -> 89.9 °C after 1 hour at -10 °C:
The low priced Quickstop thermos is made by the German company Isosteel and comes with both a screw cap and thermos mug. Despite being relatively light, it is still sturdy and is manufactured from stainless steel. This is no-frills flask with leak protection which works automatically when the mug is screwed on.
While we easily could call it ‘just a standard thermos’, this actually says quite a lot. The Isosteel Quickstop has a top-class heat retention capacity while staying cool on the outside. The only disadvantages of this thermos are that its opening is a bit small making it hard to clean and that its lid is rather slippery to handle if you're wearing gloves. Despite it coping with our leak test without problems, the thermos did end up with two small dents when we dropped it on the ground. While these drawbacks did slightly reduce the thermos’ overall score, on balance the Isosteel Quickstop remains a good value for money budget thermos for everyday use.
A both substantial and stable thermos
Price class: Medium External diameter: 70 mm Diameter opening: 88 mm Height: 262 mm Weight: 631 grams Volume: 500 ml Heat retention capacity: 100 -> 76 °C after 4 hours at room temperature, 100 -> 87 °C after 1 hour at -10 °C
The Swedish designed Primus Trailbreak Vacuum Mug is a large, stable thermos with a generous opening. Its stainless-steel construction has silicon gaskets which prevents the cup from leaking. Alongside the actual drinking cup, the thermos includes two lids - a normal lid and a ‘ClickClose’ lid for when you want to drink without taking the lid off. While this is a nice idea, the ClickClose lid isn't as easy to keep clean and can break more easily than the stopper shaped lid. This means you have more parts that you need to take care with while handling. Despite the fact that the outer cup lid on the Primus does have grip-friendly grooves, it's still quite difficult for anyone with small hands to open. The thermos has a cool outside and was robust enough to cope with both our drop testing and leak testing. The Primus Trailbreak Vacuum Mug will be a good purchase for anyone who wants a substantial thermos with a variety of different types of cup.
A thermos that will be your best friend on shorter trips
Price class: Medium External diameter: 70 mm Diameter opening: 58 mm Height: 200 mm Weight: 343 grams Volume: 532 ml Heat retention capacity: 100 -> 68.3 °C after 4 hours at room temperature, 100 -> 81.5 °C after 1 hour at -10 °C
The Hydro Flask Wide Mouth Flex is a small, lightweight and easy to manage thermos. Despite being made from stainless steel, the outside of the flask doesn't feel hot when filled with boiling liquids. The large opening makes it easy to clean compared to the other thermoses we tested. The lid has a handy rubber handle that's easy to get a grip of, even with cold, fumbling hands during a day on the ski slopes. The Wide Mouth Flex had no problems with our drop and leak testing. However, we did find the thermos to go cold relatively quickly, both in our indoor test and our outdoor test in winter temperatures. The Hydro Flask Wide Mouth Flex is therefore most suitable for shorter adventures or for your morning coffee on the way to work.
A trendy flask for people on the go
Price class: Medium External diameter: 67 mm Diameter opening: 44 mm Height: 216 mm Weight: 258 grams Volume: 355 ml Heat retention capacity: 100 -> 67.8 °C after 4 hours at room temperature, 100 -> 83.5 °C after 1 hour at -10 °C
Klean Kanteen is making a major investment in manufacturing water bottles and thermoses in stainless steel instead of plastic, with a view to reducing the environmental impact of their products. The lid on the Insulated Classic thermos is easy to use and doesn’t leak. The body of the flask doesn't get hot on the outside, but it did dent slightly during our drop testing. The thermos opening is rather small, which makes cleaning difficult, and the thermos also doesn't keep drinks hot for very long. However, the Insulated Classic gets bonus points for its innovative design and its striking colours. Above all, Klean Kanteen's Insulated Classic feels like a cool thermos that was primarily developed for city-dwellers who might a caffè latte in one hand and a laptop in the other. For this environment the thermos would be fine.
A simple, everyday thermos that is dishwasher-safe
Price class: Medium External diameter: 60 mm Diameter opening: 65 mm Height: 200 mm Weight: 275 grams Volume: 350 ml Heat retention capacity: 100 -> 54.2 °C after 4 hours at room temperature, 100 -> 75.2 °C after 1 hour at -10 °C
The Eva Solo To Go Cup is a smaller sized thermos made from stainless steel with a functional silicon click-open lid. This lid is great if you don't want to have to unscrew a cup, but also comes with a greater risk of leaking as if there's any remaining liquid in the lid, it may leak out later on. Despite the cup having a handy strap, the flask was a little bit difficult for our smaller children to open. However, the thermos is dishwasher-safe, which is unusual out of the flasks we tested and is a big plus point for anyone who doesn't like washing us their flask by hand. The thermos didn’t leak when laid on its side and didn’t break when we dropped on the ground. However, the outside did get a little warm when filled up with hot liquid and the thermos didn’t stay hot for very long. While the Eva Solo To Go Cup isn't something you'll want to rely on for a full day trip, it's fine as an easy-to-manage thermos to fill with coffee and shove in your bag when you're on the go, just as its name implies.
Whether it’s full of hot chocolate for a day out on the ski slopes, coffee for your commute or warming soup for a lunch while hiking - a thermos flask is useful in many different circumstances. The biggest advantage of a thermos is that you can always have a hot drink with you regardless of whether there are cafés or shops nearby. You save a lot of money by taking your own hot drinks with you from home.
There are currently a variety of different thermoses available to buy. Some have traditional screw cups and some have spouts to drink from. You can buy a thermos with a classical design made from grey stainless-steel, or you could choose one with an innovative shape and colourful patterns on the outside. If you have a lot of guests you could use a larger thermos jug, or you can use a smaller thermos that only contains only a single cupful of liquid if you want a hot drink during your commute.
In this test we tested relatively small, light thermoses that have capacities of around 500 ml. This size is easy to take with you and is suitable for either one or two people. All the thermoses are made from stainless steel, a tough and thoroughly tested material which is perfect for thermal flasks. We looked at the most popular models on the market, some of which are genuine classics which have been manufactured for several decades. While many of the thermoses available today are primarily intended to keep coffee hot during short walks in the park, if you want a thermos for this purpose you can pretty much buy any thermos you like. Most models can easily cope an easy task such as this. In our test, we pushed each model of thermos a little bit further. We wanted to find a thermos that could keep liquid hot during a long hike in the forest, that could thrive in winter conditions, that could tolerate being dropped on the ground, that is suitable to be used by children or someone wearing gloves and that would not leak into your rucksack. The ideal thermos also has to be easy to wash, ideally in a dishwasher, and should not consist of too many separate parts.
Our test showed that smaller and modern stainless-steel thermoses are generally very good. Ultimately, all of the thermoses we tested were satisfying products, and even the ones that didn't come out on top in our test were of relatively high quality. None of the thermoses broke during our test, and even if a few of them ended up with small dents, none of them leaked.
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