The main job of a thermos is to keep colder things cold and hotter things hot. It relies on a double-wall construction that offers insulation.
A thermos bottle is built using two vessels in the interior between which the vacuum is filled.
The flask is made using a food-grade stainless steel interior with a copper or reflective coating. The exterior of the bottle is made using stainless steel with a powdered layer of silicon.
Vacuum that is present in between the vessels works as an insulator. This prevents the heat from escaping due to conduction. The bottles come with a tight stopper or lid that prevents the transfer of heat through convection. The copper or the reflective coating works on reflecting the heat to the liquid.
This mechanism helps in maintain the beverage hot for a long time.
The same goes for colder drinks too. The stopper prevents the heat from entering the bottle. The vacuum insulator helps in preventing the heat from entering via conduction. This helps in retaining the temperature of the drink for hours.
How to Choose a Thermos – A Buying Guide
If you check online, there are a lot of thermos flasks available in the market in different designs, shapes, and sizes. You should select the shape of the thermos flask on the basis of the liquid that you want to carry in it.
Mentioned below are the most important factors that you must consider buying a thermos flask. Let’s have a look!
1.The intention of use
You can use a thermal flask for keeping both hot beverages and cold beverages. There are different models of thermos that can be used according to your requirement.
Some models of thermos come in a mug shape with a straw. These models are designed for cold drinks so that you can simply sip-in.
Thermos flasks offer multiple storage capacities. They come in different sizes – 350ml, 500ml, 750ml, or 1050ml. You can choose the size of the bottle as per your requirements.
You will find some small thermos flasks that can be used to carry extra servings of tea or coffee along with you or your morning commute. You can carry them for shorter hiking activities. However, these flasks are not great for carrying liquids in large servings for a group outing.
If you are going to places where you might not get a chance to refill the flask, it is suggested to consider a flask that offers large capacity.
3. Heat Retention
It is a very important factor. It defines the amount of time for which the flask can keep the drink hot or cold. An average flask offers a heat retention rate of 4-5 hours. However, there are some high-quality flasks that offer a heat retention rate of 12-24 hours too.
These flasks are very useful if you are going on a long drive or shorter trips. It will keep the water or soup warm for a very long time.
While selecting the bottle, check if it offers double-wall vacuum insulation or not. This feature prevents the conduction of heat. The reflective stainless steel interior prevents the heat from escaping outwards and maintaining the temperature inside the bottle.
4. Type of Insulation (Vacuum or Foam)
The most common types of insulation used in thermos flasks are – vacuum and foam.
The vacuum insulation works by preventing the transfer of heat from the outside of the bottle to the inside. It does so by creating a vacuum in the inner wall. Since there is no air, the convection does not occur and this is how the temperature of the liquid is maintained inside the bottle.
In foam insulation mechanism, the convection is prevented by using foam. It becomes very difficult for air to move around in the foam. Thus, heat cannot transfer from the outside of the bottle to the inside.
When compared, flasks with vacuum insulation maintain the temperature for a longer time than the flasks using foam insulation.
It uses double-wall construction that creates a gap (for the vacuum) between the liquid and the exterior shell of the bottle. The wall prevents the heat or cold from escaping or entering inside the bottle, thereby, maintaining the original temperature of the liquid. The only way the liquid can lose the heat is via the lid when you open and close it. But, the best products try to maintain the temperature at its best.
Selecting the right material of the thermos flask plays a major role because it decides the retention factor.
There are many materials that offer good thermal insulation. But, the double-walled stainless steel material has been proven to be the best amongst all.
Some cheaper models use plastic as thermal insulators. They are not good insulators and can keep the temperature intact only for a couple of hours.
Users prefer using thermos flasks that are made up of stainless steel because they are more durable than plastic. The stainless steel is resistant to corrosion. This ensures that the bottle won’t form rust for a long period of time. It also provides strength and is scratch-resistant. The best part about it is indoor steel can hold the vacuum isolation pressure inside the bottle.
Manufacturers also use different types of materials to make the outer casing. The most popular amongst them is plastic. It is lightweight and makes it easier to carry the bottle along with you. Some bottles also have a metal outer casing. They offer solid construction and are more practical as they are corrosion-resistant too.
An easy way to check if the thermos flask is good or not – a good thermal insulator should not get hot while you are pouring in the hot beverage. It should not sweat too when you pour a cold liquid inside.
Durability plays a key factor in determining the type of thermos flask that you want to buy. It depends on the situations that you are going to use flasks too. For example, if you are carrying the flask to any outdoor activity, chances of it accidentally falling are high. Sometimes it gets broken too due to which the hot liquid can flow out. This can be very dangerous.
Any thermos flask that loses its ability to retain the heat for a longer period is a waste of money. Thus, a flask should be made using strong and durable materials so that it keeps the vacuum intact and offer the best performance.
Most of the thermos flasks are made using stainless steel as they are strong enough to hold the vacuum. It also withstands accidents or bumps for a longer time. Another key factor is stainless steel is rust-free. Hence, it is less prone to damage.
There is one more feature with the durability of the product and that is an insulated lid. It is very difficult to design a perfect insulated lid. A perfect insulated lid is the one that is easy to use and keeps the vacuum intact inside the bottle.
Any thermos flask should be able to provide a strong and secure lid with a proper locking system. This will help in preventing any type of leakage from the bottle.
8. Delivery System
The delivery system of the flask depends on the liquid that is present inside. While some flasks come with a straw, others offer an adjustable mouthpiece or a sipping hole. Some flasks even allow you to unscrew the lid and turn it into a drinking mug.
An easy delivery system allows you to access the drink easily without spilling.
People who use it while hiking or trekking prefer a thermos flask with a carabiner loop lock to ensure that the bottle is spill-proof or leak-proof.
Manufacturers are coming up with some stylish and elegant designs that are not only durable but also light in weight.
The thermos flasks are usually constructed using 304 food-grade stainless steel material. Its interior should have a reflective copper coating and the exterior should have a silicon powdered coating. To give it an elegant and stylish look, people prefer flasks with a matte finish exterior.
An ideal thermos flask should be light in weight and should have a compact design. It should be easy to carry in your backpack’s compartment or the cup holders in the car. A thermos flask should last for a longer period and should have a durable construction.
11. 100% Food-Grade Material
Before buying a thermos flask, make sure that the flask is made up using 100% food-grade materials. 304 food-grade stainless steel is the best material to make a thermos flask. It is corrosion-free, BPA-free, and is rust-free.
This material ensures that the flask is durable. It allows a safe and secure consumption of the liquid and as it is free from chemicals or toxic elements. They are environmental-friendly too.
12. Easy to clean
It should be easy to clean the interior of the bottle. It should have a superior clean finishing that helps in preventing stains and odor. A bottle with an adjustable opening or a full mouth is always suggested as they allow easy cleaning. You can use a soft bristle brush to wash the interior of the bottle properly.
This helps in maintaining hygienic conditions and safe and healthy drinking.
Weight is always a concern while selecting the thermos flask. Heavy flasks add a lot more weight to your backpacks and it becomes inconvenient after a point. They take a lot of space too.
Look for a flask that is light in weight and does not take much space in your car or your backpack.
14. Other Features
- You should also check for the grip that the flask offers. Most of the good models offer rubber grips or a powdered-coat finish to improve the grip.
- You can also check if the bottle has a handle to carry or not. Bottles with handles are easy to carry.
- If you wish to carry the bottle along with you while running or training, you can look for bottles that come with a carrying strap or clips on the bottle. There are specially designed flasks for training. They offer a comfortable grip.
- For traveling purpose, you can select flasks that come with a slim travel tape. They fit perfectly in the cup holder of the car.
- There are some flasks that offer large capacities too. But ensure that they offer an airtight lid to prevent leakage.
- Some models offer a carrying case too. They help in preventing damage caused by leakage (just in case).
You can easily find a good-quality thermos flask for Rs.300 – 1500. Don’t go with the heavy price tag always. You can find a decent bottle with all the necessary features at an affordable price too.
At the same time, don’t go for cheaper plastic thermos flasks as they don’t offer good performance. They are not long-lasting too.
Any product that comes with a warranty proves that it is reliable. Hence, choose a thermos flask that offers a good warranty period. Usually, manufacturers offer a warranty of 6 months to 1 year.
Benefits of using a thermos flask
- It offers you a money-saving option. Rather than buying coffee again and again, you can get your own coffee and sip whenever you require the caffeine-boost.
- The flasks are portable and can be carried along with you everywhere.
- They help in reducing food wastage. Rather than throwing extra tea, you can transfer it to the flask.
- The thermos flasks are eco-friendly and help in reducing paper or plastic wastage. Not only they help in maintaining the temperature of the coffee, they also help in reducing the usage of plastic or paper cups. It can be very helpful in lowering the carbon footprint in the environment.
How to clean a thermos flask?
To clean the flask properly, you can put a tablespoon of baking soda and half a cup of vinegar into it. Shake the bottle well and throw it off in the sink.
Pour some hot water into it and leave the bottle for 10-15 minutes. Now throw this water and clean the interior with a long brush. In the ending, rinse the bottle with some salt and water to clean it completely.
Buying & Maintenance Tips
- Look for a flask that is robust and compact so that you can carry it wherever you wish to.
- To check the fragility of the flask, open the lid and check whether the vacuum glass is too close to the plastic finish. If that’s the case, don’t buy that flask.
- Check if the cork has a gasket or a circular rubber band. It is suggested to buy a flask with a double gasket as it holds the temperature for a long time. It also creates double pressure and does not allow the heat to escape.
- If there is a hot beverage inside the flask, open it very carefully to avoid burns.
- Pack only hot steaming food or ice-cold food items.
- For any food item to be safe to use, pack hot items at at least 165F or cold items below 40F. If you notice that the food is not hot enough or cold enough after opening the lid, avoid eating it as the chances of food-borne diseases are high.
- To maintain the proper temperature, pack the food just before leaving the house.
Frequently Asked Questions
The best way to improve the effectiveness of a thermos flask is pre-heating or pre-cooling. Before filling it with liquid, fill the bottle with hot water or cold water (depending on the type of liquid). Let it stand for 3-5 minutes. Rinse it off and then pour the desired liquid.
It is suggested to not use dairy products or milk in the vacuum-insulated thermos as they are prone to bacteria. Over a time period, milk can ferment and this can create a build-up of pressure. It might be a bit risky to remove the cap afterward.
Apart from this, you should not put dry ice also in a sealed container for a long period of time. In a closed space, the evaporation of CO2 from solid to gas can build an unwanted pressure inside the flask.
18/18 stainless steel is a highly sustainable and food-grade material. It is non-reactive and is composed using 18% chromium and 18% nickel and is completely safe to use.
Copper is considered as a better conductor of heat when compared to stainless steel. Thus, to improve efficiency, some manufacturers use copper in addition to stainless steel. It also helps in preventing the bottle from getting hot from the outside.
Well, usually these insulated flask bottles don’t smell bad as they are made up of superior quality materials. But, even if it smells then you can go for cleaning the bottle with baking soda or simple detergent along with water. Also, make sure that the bottle is completely dried up before you go for using it as it can still have the smell of detergent. Caution- use very less detergent to clean.
Glass bottles are not feasible to use as they come with a risk of breaking down. Also, you can’t clean the glass bottles properly and they are heavy weight. If it breaks down, it can hurt anyone and hence not much reliable but a flask is lightweight, easy to clean and doesn’t break easily.
Yes, you can store either a hot or a cold drink or beverage as a vacuum insulated flask bottle is capable of holding the temperature of your drink for as long as 24 hours.
As you know, an insulated flask bottle comes with double vacuum insulated wall. So, this wall ensures that the outside heat doesn’t come inside and thus keeps the temperature constant for as long as 24 hours.
No, not all as there are various products in the market and you can read about the best 7 insulated flask bottles in the above article. Some are liable to keep the temperature intact for as low as 6 hours while some can keep it for as long as 24 hours.
Yes but not for so long as it is a very good conductor of heat and you can see many utensils made of it in your kitchen. If you really want to invest in a bottle that can keep your water hot for many hours then go for an insulated flask bottle as it can retain the temperature of your liquid for as long as 24 hours.