Last Updated on September 12, 2021
Vacuum insulated thermos flasks are great travel accessories, they’ll keep your soup or coffee warm when going for a picnic or a hike.
But what are the rules about taking a thermos onto a plane? Are vacuum flasks a good thing to pack when traveling by air?
Let’s find out.
TSA Thermos Rules
The Transportation Security Administration runs airport security. It’s their job to stop prohibited items from getting on to planes.
I took a look at their website, the most relevant rule was about packing a coffee thermos:
Can you bring a thermos flask in carry-on luggage?
Yes, you can bring an empty thermos flask in carry-on luggage through airport security.
It must not contain liquids when you are going through security screening, but it could contain solid foods, no soups or stews.
You can also fill the thermos flask after you have passed through security.
So if you want to buy a coffee after you have cleared security you can do that and it will stay warm in your thermos to have later.
Any liquids passing through airport security must be in containers smaller than 3.4 oz and packed in your one quart-size bag. That’s why your thermos must be empty during security screening.
Can you bring a vacuum flask in checked luggage?
Yes, you can bring a vacuum flask in checked luggage.
And you can bring a thermos flask containing liquids or foods in checked bags. The liquid rules only apply to hand luggage.
Still Unsure? Ask The TSA!
You can reach out to the TSA on Twitter and ask them about your specific vacuum flask or anything else.
Paul checked if you could pack his Stanley vacuum flask for his flight.
The TSA answered that “An empty thermos is allowed in carry-on bags”.
But thermos flasks are not only used for liquids.
Rachel got confirmation that she could bring hot solid food through airport security in a stainless steel thermos food container.
That’s one way to avoid eating in airport restaurants!
Just remember the food must be solid so soups and stews are out.
Mels was worried about how she would prove her thermos was empty at the security checkpoint since it was not see-through.
Firstly your thermos flask will be scanned by the x-ray machines.
If the security officers have any concerns they might want to take a look inside your thermos flask.
The security officers always have the final say about what is or isn’t permitted to pass through the security checkpoint.
Marissa wanted to bring organic milk for her kid through airport security in a metal thermos.
While you normally can’t bring liquids over 100 ml or 3.4 oz through security you can bring milk or juice for kids.
So if your thermos contains a drink for an infant or a toddler traveling with you then you will be able to bring it in your carry-on luggage.
Let the TSA agents know what’s in your thermos and why once you reach airport security.
Autism Mumma wanted to bring hot food in a thermos for her “super fussy kiddo”. The thermos would contain hamburger, corn, and mashed potato.
This is where the rules can get a little strange.
Because the potato was mashed the TSA would not treat the contents of the thermos as “solid food”.
This means that particular thermos could only be packed in checked bags.
If the potatoes were not mashed then everything in the container would be classed as “solid food” and the thermos and its contents would be permitted through security in carry-on luggage.
Yes, that’s right! You can bring a solid potato on a plane but not a mashed potato. Keeping our skies safe has it’s quirks 🙂
So, one solution might have been to pack a potato masher and mash the potatoes after clearing security!
Also, even mashed potatoes might make it through security depending on the age of the kid and any medical conditions. The TSA frequently makes exceptions to the rules for infants or for medical conditions.
Jason wanted to bring Italian food in a thermos in his checked suitcase through airport security so he asked the TSA if he could do it.
The TSA advised him that because of the marinara sauce his meal would not be considered “solid food”.
This would mean he would need to pack his thermos containing marinara in checked baggage.
Suppose you wanted to bring spaghetti bolognese in carry-on luggage and didn’t want to pay those high fees for checked bags.
The spaghetti and the cooked ground beef could go in a thermos flask, but the marina sauce could only be in small travel-size bottles and packed with your toiletries in your one quart-size bag.
After you have cleared security simply pour the tomato sauce from your travel-sized container onto your hot ground beef and spaghetti. The meat and pasta would heat the sauce.
Voila! You just took hot spaghetti bolognese through airport security.
Anyway, I digress…
The Bottom Line
You can’t bring a thermos flask full of liquids through airport security because of the TSA liquids rule.
You can, however, fill it up with hot or cold liquids after you have made it through security.
The vacuum flask itself is perfectly safe. It’s not going to explode due to air pressure or anything like that.
If you want to take a thermos flask on a plane with a hot liquid in it you’ll need to pack it in checked luggage.