How long does a thermos keep warm?

How long does a thermos keep warm?

You want to change your lunch box and for that you thought of a thermos? You want to keep hot food in it, but you still have doubts about its capacity to keep the heat? We offer you an exhaustive answer on how long it takes for the bottle to keep the heat.

Everyone wants to eat hot food in a portable jar especially in the winter season. However, one of the main challenges is to find a container that can keep the heat in. Indeed, it would be unpleasant to prepare your hot lunch in a bowl and discover several hours later that it is cold. Thermos flasks are a healthy alternative you can try. Whether it's your breakfast, a good coffee or even a homemade soup, this is the perfect accessory we recommend.

If you want to know how long a thermos keeps warm, the answer is quite simple: between 6h and 12h depending on its use and the model of mug you have chosen.

To help you get to the bottom of the mystery behind the performance of thermos flasks, we will show you in this article how the meal box works. Better yet, you'll also get to see some of the best heat preserving thermos models.



How does a thermos work?

The functioning of a thermos allows you to better understand the temperature ranges as well as the duration of heat conservation. Better yet, it explains the performance of a water bottle capable of holding hot meals in a remarkable way.

And to understand how the accessory works, you need to know its composition.


Thermos flasks, including those from Healthy Lunch, are made from a fully reusable polypropylene plastic and stainless steel. In other words, it's an assembly of two boxes, one inside the other, but separated by a small space.

The role of the latter is quite essential in the process of maintaining heat. Indeed, this empty space serves as thermal insulation for the stainless steel bottle. It minimizes thermal conduction, which is nothing more than the flow of heat in direct contact with the ambient air.

However, this role is limited and this is where the stainless steel wall of the container inside comes in. The latter will create a reflection of heat rays and maximize them inside the bowl. By this process, the heat transfer to the outside is controlled.

Thanks to this structure, you can keep your drinks or any other liquid hot for a long time.


How long does it take for a thermos to keep warm?


The thermos usually keeps a liquid warm for at least 6 hours. This is its performance period, during which you are sure to find your food still warm. After this time, the mug slowly cools down and is at a lukewarm temperature after 12 hours. Of course, this is not a universal theory, as there are some thermos models that offer more performance.

This is the case with the insulated water bottles from our Healthy Lunch store. Indeed, they have undergone several tests with boiling water inside. After 6 hours, we noticed that the temperature of the water was still so high that you could burn yourself. Even better, the water was still hot after 12 hours and could even be used for coffee.

It is important to note that the heat storage of an insulated mug depends on its capacity. It seems obvious that a small flask (300 ml) will not be able to keep warm as long as a medium-sized bottle (500 ml). On the other hand, a 1-liter isothermal mug can easily keep warm at a temperature of more than 70°C for at least 7 hours.

Further on, some additional tests exist to better explain the temperature evolution within the food box. Find here the results after an analysis performed on a 0.5 liter thermos containing hot water.

  •     Initial temperature : 94.6°C
  •     After 2 hours : 90.1°C
  •     After 4 hours : 86.6 °C
  •     After 6 hours: 83.2°C
  •     After 24 hours : 65.1°C


How to keep the heat in a thermos longer?

Now that you have mastered the scientific secret of the thermos, it would be interesting to learn how to keep the heat inside as long as possible. To do this, you will need a few foolproof tips.

Warm the thermos before use

The first way to slow down the cooling of the contents of your thermos is to heat it up beforehand. This

reduces heat loss. To do this, simply pour boiling water into the stainless steel bottle. It is important that the water is extremely hot so that it can better soak the walls of the thermos.

Then, wait about 10 minutes and empty the water while taking care to quickly wipe the inside. Obviously, this last instruction loses its meaning if you intend to put a liquid meal in the thermos.

Use a hot drink

If you don't want to drink hot chocolate or tea right away, it is recommended to prepare it hot. Then pour it to the brim of the container. In fact, the hotter the food is and the more internal space it occupies, the more it will retain its temperature inside the mug.

Close the lid tightly

All thermos jugs have a lid that must be sealed. Naturally, this prevents the penetration of external air that is supposed to cool your drink. Also, we recommend that you only open the cap when you are ready to drink.

Bring a cooler bag

As their names clearly indicate, insulated bags are excellent thermal insulators. By storing your thermos in it, you ensure that your food is warmer. Technically, the inside will still be warm for at least 24 hours.


Which thermos keeps the heat for a long time?

Find in this section a top 3 of our best thermos flasks for a long term preservation of your hot food.

The Cat Stainless Steel Flask

Tea Thermos Celestial Cat

You have a weakness for cats and hot drinks? This thermos will certainly please you. Indeed, it is one of the rare products in our store to keep its temperature regulation properties for a long time. Particularly designed in high quality stainless steel, it will keep your food as hot as you want. In addition, you can count on its double-walled vacuum insulation.

More precisely, it lasts for 12 hours to keep your food warm, no matter what the external weather conditions are.

Offering a capacity of 500 ml, its wide opening ensures that you will not have trouble getting your food out. Moreover, the gourd has a tea filter if you plan to keep your tea warm for a long time.

The Lunch Box Persimmon Soup

Lunch Box Soup Kaki

This high temperature resistant tupperware keeps your soups warm for at least 12 hours. It owes such performance to the thermal insulation of its stainless steel con

struction. Specifically, the lunch box has a double layer vacuum insulated wall. Thus, the heat loss by conduction is extremely reduced.

Apart from these technical details, remember that you can carry meals with an average capacity of 350 ml. Moreover, its compact size allows you to take it everywhere: 9 cm wide and 15 cm high. In addition, the bottle has a hermetic and insulated lid that traps heat properly inside.

If you have children, this model could make a great gift to take to school. Whether it's stew, noodles or chicken broth, you'll be sure to please your little ones at break time.

The Blue Isothermal Lunch Box

Lunch Box Isotherm Blue

With a good capacity of 750 ml, this isothermal mug not only carries liquid food, but also hearty meals. It is ideal to accompany you at work or in seminars. No matter how long your meetings last, the large mug will always keep your food warm until you open it.

In fact, its impressive thermal technology allows it to confidently keep your drinks and menus warm for up to 12 hours. It's a six-fold thermal insulation that reinforces its durable stainless steel interior. Better yet, its outer container is also made of PP and remains BPA and PVC free. In a sentence, this is simply one of the best thermoses on the market today.

We don't forget to mention that it comes with a foldable spoon and an insulated bag. When you're done using it, you can easily clean it, as it's dishwasher safe like a plate.

Whenever you need to take a hot food with you, don't hesitate to think about our insulated thermos. In short, we understand that they are all insulating and capable of keeping warm between 12 hours and 24 hours depending on the model.

Insulated Lunch Box

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