Yes, you can take a Hydroflask with you on a plane. The flask should not contain any liquid while passing through security screening.
The TSA encourages passengers to bring an empty reusable water bottle as a part of the Go Green campaign. So, you don't have to hesitate to bring a flask on the plane.
However, there are a few things or steps you need to follow to avoid unnecessary problems with security.
1. Take an Empty Flask
The thermoflask needs to be emptied before you send it through security checking. Once it passes through, you can refill the container at the airport.
If you are wondering about filling your flask with your favorite tea or coffee while leaving the house, then immediately drop the idea. The container needs to be empty so that the authorities are able to see the inside of it.
TSA has a rule regarding liquid called the 3-1-1 rule which basically translates: No bottle larger than three ounces (or 100ml), no more bottles which cannot fit in a clear plastic one-quart bag, and one bag per person. This means you can carry your thermos but you cannot put any sort of liquid in it before security screening.
If your flask is obstructing the views of the TSA agents and giving them cause for concern, then your flight experience may turn unpleasant even before you board.
2. Buy a Branded Flask
If you're planning to take a thermoflask with you to the airport make sure to check the label. Only take a branded container with you.
Some of the popular brands include Hydro Flask, CamelBak, S'well, Cirkul, Nalgene, and Que. You can get your hands on these insulated water containers at Walmart and other online shopping sites.
Brands project value among the customers and they are extremely lightweight. While you are carrying one of these branded thermoses, TSA agents might just pass it without much attention.
An unbranded thermos is thick and has many layers. The security personnel might suspect that you are hiding things between those layers. On the other hand, branded thermos have very few layers, and are built with superior materials which makes them thin and lightweight.
3. Avoid Maximum Filling
Your hydroflask needs to empty at the security checkpoint. You can fill the container before boarding the plane.
However, makes sure you do not fill the container at its max capacity. This causes a problem when the plane takes off because at that point the cabin pressure rises slowly.
Not a science lesson, just a simple reminder that cabin pressure increases after the plane gains altitude. As a result, the air is trapped inside the container.
Imagine the plane is cruising at 33,000 feet and you finally decide to open your fully-filled flask. The built-in pressure inside the container releases with a sudden force if you open it right away. It is wise to open your thermos slowly.
Likewise, do not use a straw on the plane. The pressure causes the liquid to rise through the straw rapidly causing it to spill all over. You might even ruin the mood of the passenger next to you, unintentionally.
