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Can Thermos Go in the Dishwasher? (Quick Answers)

You don’t know the endless perks of owning a thermos until you own one. Thermos, whether they are flasks, mugs, or food carriers, keep your food hot and your liquids cold when you need them to.

Washing these can be an extra chore. Could you make your life easier by simply tossing the thermos into the dishwasher? That’s not a great idea!

Thermos go in the dishwasher

Thermos flasks, mugs, or containers are only top-rack dishwashers safe. However, the thermos should be hand washed since the high heat and strong detergents from the dishwasher can damage the insulation properties of the thermos. Glass thermos should not be put into the dishwasher at all.

But can all thermos go up in the dishwasher? Let’s find out.

Thermos flasks:

Thermos flasks come in all shapes, sizes, and types. Typically, the most common type of thermos flasks that you might have used is the stainless-steel vacuum insulated flasks.

These flasks have a stainless-steel exterior body, and a vacuum spacing layer. This layer is sandwiched between two walls to keep the heat or cool trapped.

These flasks with rubber and plastic lids are only dishwasher safe if put in the top rack of the dishwasher.

The lids of these flasks are more prone to damage when washed in the dishwasher due to the material the lids are made of. 

Keeping a thermos flask in the bottom rack can cause permanent damage in only one wash.

Most companies recommend hand washing for the durability of the flask. Glass thermos flasks, on the other hand, is not dishwasher safe and should only be washed by hand.

Thermos containers:

Thermos containers are primarily used to keep food hot. In school and offices, people pack up hot food for long hours.

Thermos containers, too are only safe to be put into the dishwasher top rack. Since containers carry food instead of hot liquid, thorough cleaning is required, that too daily if used.

For that handwashing is the best option along with the use of vinegar and water solution for better cleansing. The strong detergents in the dishwasher would also damage the appearance of your thermos container.

Mostly the high heat and aggressive washing may damage the insulating property of the container.

Thermos mugs:

Thermos mugs are a traveler’s best friend but once the trip is done and you’re back home, you might be tempted to put the thermos mug into the dishwasher.

It is recommended that thermos mugs are hand washed to keep the integrity and efficiency of the mug from depreciating.

Although you might not notice any changes to your mugs after the first time it gets washed in the dishwasher, except if you put the mug into the washer a few more times.

Chances are the high heat and harsh soaps of the dishwasher would ruin the vacuum space between the double walls.

Thermos water bottles:

Thermos water bottles are not so different from thermos flasks except those bottles are smaller in size.

Thermos bottles are also used, and hence opened and closed more often than thermos flasks. The walls and the lids of the thermos water bottles may be thinner and more prone to damage in the dishwasher.

Without the lid, you may put the thermos water bottles in the top rack of the dishwasher only so that excessive heat does not damage the lid.

Is the kid’s thermos water bottle dishwasher safe?

Whether a kid’s thermos water bottle is dishwasher safe or not largely depends on the company that manufactured the flask. You would need to read the manual to know whether the thermos water bottle is safe to toss into the dishwasher.

While some mean that their thermos should only be hand washed, others label it dishwasher safe.

Since it’s a thermos with a lid, it would be safest to keep the lid or other accessories out before putting the flask in the dishwasher, that too only on the top shelf. The kid’s thermos is tinier in size and may be handled more roughly by kids.

This means you would need to make sure that the lid of the water bottle is not damaged by the heat cycles of the dishwasher.

Some brands specifically mention how you would need to wash the thermos water bottle, emphasizing how abrasive cleansers like that of dishwashers may compromise the insulation and appearance of the flask.

Why aren’t thermos dishwasher safe?

Now that you know how you can put a few types of thermos in the dishwasher while you need to handwash a few others, it is important to know why.

Here are explanations are to why you can put some thermos into the washers, while some others may immediately get damaged.


It does not matter whether it’s a thermos flask, a container, or a small thermos mug, if the brand comes with an instruction to keep the thermos away from the dishwasher, you would have to.

One reason why a thermos may not be dishwasher safe is the material used to contrast the thermos.

For instance, if you have a glassware thermos that you want to put into the dishwasher, the possibilities are your flask would lose all its insulation properties just after one wash.

No bottom rack placing:

It is specifically mentioned that thermos flasks and containers are only top rack dishwasher safe. No thermos can or should be put into the bottom rack of the dishwasher.

This is because in dishwashers, the heat is radiated from the lower compartment, and that is where the temperature is much higher. When thermos is exposed to such heat, the insulation between the walls is immediately damaged. 

Abrasive damage thermos:

Thermos bottles and mugs also don’t fair well when washed with abrasive or strong detergents.

The detergents in dishwashers are high in chemicals and abrasive, possessing the chance to ruin both the appearance and longevity of the thermos.

Keep the parts apart:

Although it is possible to wash thermos in the dishwasher top rack, you should keep the lids and parts out, unless otherwise advised in the manual.

In many cases, the lids are made of lead seals, which could build up mold in the long run if exposed to so much heat.

Where should thermos go in the dishwasher?

A thermos can only go into the top rack of the dishwasher. Whenever brands label and put instructions as to whether a thermos is dishwasher safe or not, they specially mention that the flask is “top rack dishwasher safe”.

In the top rack, the heat from the water subsides and reaches a somewhat moderate temperature. That temperature, although gets the job done is not detrimental to the durability of the thermos.

At the bottom rack, the heat is radiated off just below and hence the temperature of the water may be more than the thermos material is built to endure.

In most cases the high heat damages the insulating properties, and mainly the vacuum seal, compromising the insulation gap which keeps the contents inside hot or cold.

How do you clean a thermos flask in a dishwasher?

Although it is recommended that you handwash your thermos flask as many times as possible if you’re someone who wants to clean a thermos flask in the dishwasher.

You would need to know the right steps. Here is how you clean a thermos flask in the dishwasher.

Read instructions:

At first you would need to read the manufacturer’s instructions to make sure that your thermos flask is indeed dishwasher safe. If anywhere it mentions, “handwash only”, you would not want to put the flask in the dishwasher. If you have a stainless-steel thermos flask, enlighten yourself on whether the stopper, lids, or any other part is safe to be put into the dishwasher.


If your thermos flask is too dirty and needs extra cleaning, presoak the flask, with vinegar and water solution before tossing it in the dishwasher.

Remove stopper:

Now you would want to take off the stopper after you dismantle the top. Here you would also want to open the sprout as needed.

Use top rack:

Always remember to use the top shelf of the dishwasher. If there are other dishes in the top rack, empty them up and create space for your thermos and stopper.

Face away from water:

Place the flask in such a way that it faces away from the direct outburst of heated water.

Keep the heat safe:

If your dishwasher allows you to, keep the temperature regulated at safe heat. Use nonabrasive detergent for your thermos flask. After washing, make sure to dry the flask, lid, and stopper completely.

Final Thoughts

To be even more specific, a thermos is dishwasher safe only when put into the top rack. Additionally, there are parts and accessories to the thermos that may not be dishwasher safe. There are other types of glass thermos that are not safe to be tossed into the machine.