Can I Bring a Hydro Flask or Thermos on the Plane?

Do we need to drink eight 8-ounce glasses of water a day to stay healthy?

What all scientists agree on is that consuming a sufficient quantity of liquids is very important for the body to function properly.

Now to answer your question:

As a general rule, you can bring a hydro flask or thermos on the plane in either your carry-on or checked luggage. The only problem is that the hydro flask or other container you bring with you must be completely empty at the security screening.

This is not a problem for me since I only drink water and refill my flask at the airport.

But should you want to bring your favorite tea or coffee, you’ll have to forget that idea. T.S.A. agents or other air authorities must be able to see the whole inside of the container.

If your container doesn’t allow this because of its construction, you shouldn’t try to board the plane with it. This is the main reason you will find people on Twitter complaining that their water container was taken from them.

I recommend that you buy a hydro flask or thermos from a popular brand because T.S.A. agents won’t give it too much attention, and T.S.A. mentions everywhere they can that: “The final decision rests with the T.S.A. officer on whether an item is allowed through the checkpoint.”

So don’t try to give T.S.A. agents the motive to make your flight unpleasant.

Related: Can You Bring A Metal Water Bottle On A Plane

If your thermos is not from a well-known brand, then at least don’t bring a thermos that is too thick because T.S.A. agents might think there is something hidden between the layers.

Old thermoses tend to be more robust because of how they were manufactured. Nowadays, making a good thermos involves modern and light materials, thus making it thinner and more lightweight than previous designs.

As a side note, I wrote an article about the rules for bringing lighters on planes which you can find here.

If you want to make small talk with your T.S.A. agent, you could tell him that during WW2, Italy deployed the AR-4 bombs known as “thermos bombs” because of their resemblance to thermos bottles.

On second thought, maybe you shouldn’t mention this at all at a security screening :).

After passing the security checkpoint, you can fill your hydro flask or thermos with whatever liquid you desire.

Your container doesn’t need to be empty when you are boarding the airplane; it only needs to be empty at the checkpoint.

There is a little trick that can improve the airport water’s taste.

T.S.A. rules allow you to bring a few small bottles, each containing 3.4 ounces of liquid in a 1-quart size bag, and I filled one of them with a drink syrup. Once I passed the checkpoint, I poured the syrup into my hydro flask and filled it with water.

I use Teisseire concentrated mint syrup at a ratio of one part syrup with nine parts water.

You can use whatever brand or flavor you like. If you travel frequently and buy soda or other drinks, this will save you a lot of money over the long term.

About three years ago, I met a fellow traveler who brought concentrated coffee syrup or something similar in his toiletries bag; the final product tasted like iced coffee.

I guess he found a way to avoid drinking that awful coffee that airlines offer nowadays.

Call me picky, but I think coffee should be made the right way and not from some concentrated stuff that comes straight from Dexter’s Laboratory. 

Hydro flask and airplane pressure

Before boarding the plane, don’t fill the hydro flask to the max. The problem with filling it to the brim is the cabin pressure that will rise slowly after the plane takes off.

I won’t bore you with the science of cabin pressure, but I will tell you that the higher the altitude, the higher the pressure inside the plane is.

If your plane is over 30,000 feet up and you haven’t opened the container at a lower altitude, you should open it in a way that will allow the built-up pressure inside to be released slowly.

If your hydro flask has a button for the straw, don’t use it because you will spray water on yourself or other passengers.

Cheap hydro flasks might start leaking when the pressure inside the airplane reaches a certain point.

Therefore, if the hydro flask is in your carry-on, you should check it for leaks before the plane reaches its cruising altitude.

If you haven’t bought your hydro flask or thermos yet, then you should buy one only from well-known shops because some models are counterfeited, and you might not be able to spot the difference between them.

F.A.Q.

What is the maximum size of the hydro flask or thermos you can bring on the plane?

There is no size limit for a container that you can bring on board the plane. So if your thermos or hydro flask fits in your checked luggage or carry-on, then you shouldn’t have to worry about its size.

How many containers can you take on a plane?

There is no limit to the number of containers you can bring. Of course, showing up at the checkpoint with ten hydro flasks might be a red flag for the T.S.A., but this shouldn’t be reason enough to stop you from getting through.

How many years does a hydro flask last?

A high-quality hydro flask should last you more than ten years. It is not about how long the container will last you; it’s about how long the insulated material will last. Usually, the insulating material is the first component that will break.

If you are not constantly dropping your container on the floor, then your hydro flask should stay in working order for a long time.

Once cracks appear in the insulating material, your drinks will not stay hot or cold for the same amount of time you were accustomed to. Quality hydro flasks should keep their insulation properties for more than five years.

As with any other product, exceptions can occur. For example, in online forums, you will find people complaining about their hydro flasks losing their insulating properties after a couple of months. Most of the time, they neglect to mention that they dropped it on the floor multiple times.

You might notice that some companies in this business offer crazy warranties like 50, and even up to 100, years.

Their school of thought is that once they sell a hydro flask and it breaks after 5+ years, most customers will not go through the hoops of sending back their old flask to be repaired or replaced; instead, they will buy a new one.

How to test a hydro flask’s insulation

If your hydro flask is not keeping your water cold or hot, the insulation is likely the culprit.

Testing to see if your hydro flask is still insulated is easy. Pour hot water into your container and don’t close it.

Wait a couple of minutes and then touch the outside of the container. If the container is warm to the touch, your insulation is compromised.

Usually, this defect is covered by the manufacturer’s warranty. If your container is not warm, this means that most likely the cap is damaged, and you will need to replace it.

If you are buying a hydro flask or thermos for the first time, then my advice is to buy a vacuum-insulated one.

A vacuum-insulated container will keep your drink at the temperature you desire longer than typical insulation, and it seems that the insulation will also last longer.

How often should you wash your hydro flask?

The answer depends on what you are putting in it. If it’s coffee or flavored water, I recommend washing it after every use.

If you don’t have the means to wash it, try to rinse it with clean water. If it’s only water, you should wash it once every couple of days. 

Can the inside of the hydro flask rust?

Yes. I know you probably think a typical hydro flask shouldn’t rust. The majority of hydro flasks on the market are made from stainless steel, so most people think they shouldn’t rust.

I don’t know where it came from, but there is a common misconception that stainless steel does not rust. Unfortunately, stainless steel does rust, but only in specific conditions.

There are a couple of reasons why a hydro flask might rust:

1. The hydro flask you own is counterfeited or made with low-quality materials.

I won’t bore you with the process of manufacturing stainless steel; I’ll just say that there are countless stainless steel alloys on the market nowadays.

If your flask was made from low-grade stainless steel, then it will rust.

Some of the cheap flasks are susceptible to damage even from phosphoric acid.

This information may not seem helpful because you’re not putting straight phosphoric acid in your hydro flask.

That may be true, but phosphoric acid is a substance that is used fairly regularly in the sugary drink industry and some detergents.

For example, phosphoric acid is an ingredient in Coca-Cola. 

2. Heat and cleaning solutions.

Repetitive use with hot drinks over a long period of time will make your stainless steel interior lose its anti-corrosive properties.

The solution, in this case, is simple: wait a minute before pouring your boiled drink into the container. A few degrees lower will prevent rusting.

It turns out that it’s more about the cleaning solution. For example, some cleaning solutions contain small amounts of acids that damage stainless steel over time.

You should avoid using corrosive cleaning solutions or detergents to wash the inside of your hydro flask.

Most hydro flask manufacturers offer a warranty that covers rust damage. So it shouldn’t be a problem getting your product replaced with another.

Can you bring a Yeti cup on a plane?

Yes, you can bring a Yeti cup on the plane either in your carry-on or checked luggage.

The rules are the same; the Yeti cup should be empty at the security checkpoint.