Can You Put a Thermos Flask in the Dishwasher

In today’s fast-paced world, convenience is key when it comes to household chores. One such chore is cleaning, and the dishwasher has become a go-to appliance for many. But what about items like thermos flasks? Can you simply toss them in the dishwasher, or is it a recipe for disaster? In this article, we will delve into the intricacies of cleaning thermos flasks and whether it’s safe to put them in the dishwasher.

Understanding Thermos Flasks

Before we jump into the dishwasher debate, let’s take a moment to understand what a thermos flask is and how it works. Thermos flasks, also known as vacuum flasks or insulated bottles, are designed to keep beverages at their desired temperature for an extended period. They consist of two walls with a vacuum in between, which minimizes heat transfer. This ingenious design is what keeps your coffee piping hot or your iced tea refreshingly cold for hours on end.

The Dishwasher Dilemma

Cleaning Methods

When it comes to cleaning thermos flasks, there are generally two methods: hand washing and using a dishwasher.

Hand Washing

Hand washing is the traditional and safest way to clean a thermos flask. Here’s how you can do it:

Step 1 – Empty the Flask

Before cleaning, make sure the flask is empty and free of any leftover liquids.

Step 2 – Prepare Soapy Water

Fill the flask with warm, soapy water. Use a bottle brush to scrub the interior, paying extra attention to any stained or odorous areas.

Step 3 – Rinse Thoroughly

After scrubbing, rinse the flask thoroughly with clean water to remove all soap residue.

Step 4 – Air Dry

Leave the flask open and upside down to air dry completely.

Dishwasher Usage

Many modern thermos flasks are advertised as dishwasher safe, but there are some caveats to consider.

Check the Manufacturer’s Instructions

Always check the manufacturer’s instructions before attempting to put your thermos flask in the dishwasher. Some flasks may have specific cleaning guidelines that differ from others.

Avoid High Temperatures

If your flask is dishwasher safe, use the top rack and choose a gentle cycle with cooler water temperatures. High heat can damage the seals and insulation.

Don’t Use Harsh Detergents

Opt for mild, eco-friendly detergents to prevent any chemical reactions that could affect the flask’s integrity.

The Pros and Cons

Pros of Dishwasher Cleaning

Putting your thermos flask in the dishwasher can have some advantages:

  • Convenience: It saves time and effort compared to hand washing.
  • Thorough Cleaning: The dishwasher can reach places that are hard to clean by hand.

Cons of Dishwasher Cleaning

However, there are also downsides to using the dishwasher:

  • Risk of Damage: High heat and strong detergents can potentially damage the flask.
  • Decreased Lifespan: Frequent dishwasher use may reduce the lifespan of your thermos flask.


In conclusion, whether you can put a thermos flask in the dishwasher depends on the manufacturer’s guidelines and the specific model of the flask. While some flasks are designed to withstand dishwasher cleaning, others are not. It’s crucial to check the instructions that come with your flask to ensure its longevity and performance.

If in doubt, it’s always safer to stick with the traditional method of hand washing. This not only preserves your flask but also ensures that it continues to keep your beverages at the perfect temperature for a long time.

Now, for some frequently asked questions:


1. Can I put a stainless steel thermos flask in the dishwasher?

It’s best to check the manufacturer’s instructions for your specific flask. Some stainless steel flasks are dishwasher safe, while others may not be.

2. Will using the dishwasher affect the insulation of my thermos flask?

Frequent dishwasher use with high temperatures can potentially affect the insulation of your thermos flask, reducing its effectiveness over time.

3. What should I do if my thermos flask has an unpleasant odor?

If your flask develops an odor, try cleaning it with a mixture of warm water and baking soda. Rinse thoroughly and allow it to air dry.

4. Can I put the cap or lid of my thermos flask in the dishwasher?

The cap or lid of your thermos flask may be dishwasher safe, but it’s always a good idea to check the manufacturer’s instructions to be sure.

5. How often should I clean my thermos flask?

Regular cleaning after each use is recommended to maintain the flask’s hygiene and performance.

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