Did you know that you can put a thermos flask into the dishwasher? It’s true. Many people don’t know that it’s possible to do this because they periodically forget about it, but it is quite easy to do. The only problem with putting your thermos flask in the dishwasher is the dirt on it. Clean it with mild soap and water before dishwashing it.

How Does the Dishwasher Clean Utensils? 

1. The appliance or utensil is inserted into the dishwasher.

2. Hot water is poured into the machine and a detergent is added to the water.

3. The machine is switched on.

4. Tubes inside the dishwasher circulate hot water and detergent to clean the utensils.

5. In some machines, a high-pressure pump forces hot steam through an opening in the bottom of the utensil to remove food particles from within it.

6. The utensil is then washed by a spray cabinet underneath.

7. The utensil is then held under the spray cabinet to remove any remaining food particles or moisture from it.

Ways To Clean A Thermos Flask 

1. Hot Water and a Mild Dishwashing Detergent.

2. Use an Ammonia-Free Detergent.

3. Use a Cleaning Spray.

4. Use a Cleaning Sponge.

5. Use a Cleaning Brush to Clean the Flask Inside Out. 

Why Should You Clean The Thermos Flask? 

Dead Bugs 

When you pop outside for a picnic in the summertime, rely on your thermos to hold cold drinks. But if you leave it out for too long, your drink could become infested with flies and other bugs.

Food Residue 

If you use a thermos to store hot food, the container may come into contact with grease or oil. It can leave a funny taste in your water after a while.


If you’ve noticed some leakage around your Thermos’ edges, it could be time to clean it inside out. 


If you leave a thermos in a cupboard for months on end, the container will inevitably pick up dust and dirt. This would require you to clean the thermos now and then manually, or you could use a dishwasher for it.

Is the Dishwasher Safe to Use?

Thermos flasks are generally dishwasher-safe for most situations. However, if the thermos has been dropped or subjected to a lot of wear, you should scrutinize it before putting it in the dishwasher. 

Tips for Cleaning a Thermos Flask

1. Rinse it thoroughly to remove any remaining debris from the cold.

2. Place it in a dishwasher on a normal cycle to eliminate all food particles or moisture from it.

3. Clean the bottle and lid with mild soap and water and brush it inside out.

4. Brush the outside of the lid with a soft toothbrush to remove any remaining food particles from it.

5. Use a clean cloth to wipe off all dirt and food particles from the rest of the flask, including the interior.

6. If you wish, use an ammonia-free dishwashing detergent or spray it with a product such as Bon Ami and water to remove any grease and flavorings from your thermos’s surface. Then re-wash it using hot water and dishwasher detergent.

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So, you can safely put your thermos flasks into the dishwasher. However, you must clean it beforehand to remove any dirt or food particles that might remain on the flask. One more thing, you should always clean the thermos flask regularly to ensure better health and hygiene. This will ensure a better quality of water in your flasks for longer periods of time. It is recommended that you wash your flasks in hot soapy water regularly to prevent the accumulation of germs over time.

Frequently Asked Questions

Q. I love using my thermos flask at work, but I don’t have a dishwasher. Can I wash it in the sink?

A. No problem, you can easily wash your thermos flask in the sink. However, you should ensure that it is washed thoroughly to remove any unwanted deposits on it. Also, keep in mind that water could get trapped inside the bottle if you store it upside down for too long, so be sure to empty it after every wash cycle.

Q. Can I put my Thermos in the freezer?

A. No, this will cause the thermos flask to crack or shatter. Furthermore, you should not freeze a thermos because the expansion of liquids could cause the thermos flask to burst. Putting a hot thermos in the freezer will also cause it to crack or shatter.