A Thermos (also known as a vacuum flask or Dewar flask) is an insulating storage container that keeps contents hot or cold for extended periods.
Thermos bottles are commonly used to carry hot coffee, tea, soup, or cold drinks. But can you actually put a Thermos in the dishwasher to clean it? Let’s take a closer look.
How Thermos Bottles Work
A Thermos uses vacuum insulation to limit heat transfer between the inside and outside of the bottle. There are two nested glass or metal bottles sealed together with a vacuum between them. The vacuum minimizes conductive heat transfer. The inner bottle is silvered to reduce radiative heat transfer. This combination keeps the contents hot or cold for hours.
Why You May Want to Wash a Thermos in the Dishwasher
There are several reasons why you may want to wash your Thermos in the dishwasher:
- Convenience – It can be much easier to just place it in the dishwasher rather than handwash it. This saves time and effort.
- Thorough cleaning – A dishwasher can clean hard-to-reach spots and remove stuck-on food residue. The high pressure spray can clean the inside better than handwashing.
- Sanitization – The hot water and detergent in a dishwasher can sanitize the Thermos, killing bacteria. This is important if you use it for soups, baby bottles, etc.
Is It Safe to Put a Thermos in the dishwasher?
The short answer is no. Thermoses are generally not dishwasher safe. The high heat and pressure of the water jets inside a dishwasher can damage the vacuum seal and insulation of a Thermos over time. The dishwasher’s heat and moisture can also corrode the inner and outer bottles.
Most Thermos manufacturers do not recommend putting their bottles in dishwasher. The extreme conditions are too harsh for the sensitive vacuum insulation to withstand. With repeated dishwashing, the performance and lifespan of the Thermos will deteriorate rapidly.
However, some specific Thermos models indicate they are “top rack dishwasher safe”. But in general, the dishwasher can degrade the signature Thermos insulation, so handwashing is best for longevity.
Tips for Handwashing a Thermos
Since the dishwasher is too harsh, the best way to wash a Thermos is by hand:
- Rinse thoroughly – Use hot water to rinse out any remaining liquid and loose food bits from the Thermos.
- Use mild detergent – Wash with a soft sponge, cloth, or brush using a mild detergent and hot water. Avoid abrasive scouring pads.
- Clean the inner bottle – Use a narrow bottle brush to scrub inside the inner bottle if needed. This reaches the spots a sponge can’t.
- Rinse well – Rinse thoroughly with clean, hot water to remove all soap residue. Soap remnants can affect the Thermos taste.
- Air dry completely – Allow the Thermos to completely air dry with the lids off before reassembling. Trapped moisture can encourage bacterial growth.
Dishwasher Risks to Avoid
To preserve your Thermos for maximum performance and longevity, avoid these dishwasher risks:
- High heat can damage the vacuum seal over time.
- Intense water jets can dislodge interior insulation.
- Moisture can corrode the glass or metal interior of the bottle.
- Chemical detergents are harsher than handwashing soap.
- Top rack positioning still exposes it to high heat and water pressure.
- Repeated dishwashing deteriorates Thermos performance quickly.
Alternative Cleaning Methods
If you want a more thorough cleaning, here are some alternative methods other than the dishwasher to consider:
- Vinegar rinse – Mix equal parts vinegar and water, boil, then pour into a thermos and let soak for an hour. Rinse well. The vinegar disinfects and removes odors.
- Baking soda scrub – Make a paste of baking soda and water. Use a brush to scrub the inside of the Thermos. Rinse thoroughly after scrubbing.
- Denture tablets – Drop 1-2 denture cleaning tablets into the filled Thermos. Let soak overnight, then rinse well in the morning. The tablets disinfect and clean.
- Bottle sterilizer – Use an electric bottle sterilizer or UV bottle sanitizer designed for baby bottles. These fully disinfect the Thermos interior.
FAQs About Putting Thermos in the Dishwasher
Still have some questions about washing a Thermos in the dishwasher? Here are answers to some frequently asked questions:
Is it okay to put a Thermos in the dishwasher occasionally?
No, even occasionally putting it in the dishwasher can damage the vacuum seal over time. It’s best to always handwash to be safe.
What if I use the top rack only?
The top rack is still exposed to high heat, steam, and water jets. Top rack placement can still ruin the Thermos insulation.
Can I put a stainless steel Thermos in the dishwasher?
Stainless steel models have more durable exteriors, but the interior glass bottle is still vulnerable. Handwashing is still best for stainless steel versions.
Is the dishwasher safe for Thermos food jars?
Food jars may be more durable than drink bottles, but dishwasher risks still apply. Handwashing ensures their best performance.
How can you tell if a dishwasher has ruined a Thermos?
Check if it keeps drinks hot or cold for less time than before. Also listen for air leaking when opened; this indicates a broken vacuum seal.
The Bottom Line
Thermoses rely on delicate vacuum insulation and should never be placed in the dishwasher. The high heat, pressure spray, and moisture are too harsh and can quickly degrade the performance of a Thermos.
To protect your Thermos and extend its lifespan, always wash it by hand with mild soap and hot water instead. Handle your Thermos with care for optimal insulation.
Hi, I’m Julie, the passionate foodie and founder of Juliesfamilykitchen.com. I created this blog out of a drive to prove someone wrong, and then I realized how much I truly enjoy cooking and trying new recipes. In my free time, when I’m not running around after my kids or spending quality time with my partner, you can usually find me in the kitchen experimenting with new dishes.