Can You Put Boiling Water in a Hydro Flask?

Hydro Flasks are great at keeping things cold, but can you put boiling water in a Hydro Flask?

Maybe you want to have hot coffee, hot chocolate or a hot tea later in the day or maybe you want to fill your Hydro Flask up with boiling water in the morning so you can make some instant ramen noodles for lunch.

Well there is some good news:

You can safely put boiling water in a Hydro Flask without causing damage to it. The boiling water will stay hot enough for coffee or instant noodles for around 6-12 hours or even longer in the right conditions.

So if you want to put boiling water in your Hydro Flask then go ahead, they are designed to easily handle boiling water and to easily keep it warm all day long.

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Will Putting Boiling Water In a Hydro Flask Damage It?

No, putting boiling water inside a Hydro Flask bottle is unlikely to damage it. The stainless steel it is made out of can easily handle the heat and the vacuum insulation will keep the outside from getting hot or the vacuum seal from getting ruined.

This article states that stainless steel can handle temperatures of up to 1,598°F (870°C) intermittently without it causing any damage.

While I don't advise putting water THAT hot in your Hydro Flask the 212°F (100°C) temperature of boiling water (or maybe slightly highly) is well below the threshold of the stainless steel.

However, submerging your Hydro Flask in boiling water so that the outside of the bottle is completely covered in boiling water may cause damage. It may damage the paint and cause it to discolor but more importantly it may damage the seal holding in the vacuum.

If that seal breaks then the vacuum between the inner and outer wall of the Hydro Flask will fill up with air and your Hydro Flask will no longer be insulating.

How Long Will Boiling Water Stay Hot In a Hydro Flask?

If you put boiling water in a Hydro Flask it can easily stay hot enough for tea, coffee or even making a hot meal at lunchtime.

If you put boiling water in a Hydro Flask bottle and keep the lid closed then it should remain too hot to drink for at least 6 hours, cooling down to a more lukewarm temperature around 12 hours. To keep your water hot for longer preheat the inside of your Hydro Flask first.

Here are some comments from this reddit post on people's experiences:

If you put boiling water in there at breakfast and don't open it up again until lunch it'll still be too hot to drink.

I regularly brew tea 6-8 hours after putting boiling water in my 40oz bottle. Breakfast to lunch time should be no problem.

Below is a video where someone talks about their experiment with boiling water in a Hydro Flask. They live at altitude so the temperatures for boiling water is lower there so it does skew the results a bit but it's still interesting to watch:

Can You Keep Water Boiling in a Hydro Flask?

No, a Hydro Flask will not keep water at boiling temperature above 212°F (100°C). There is no heating element in the Hydro Flask so while it will stay extremely hot for a long time it will quickly stop boiling as soon as you pour it in.

You can keep your water closer to boiling temperature for longer by first pre-heating the inside of your Hydro Flask bottle or mug.

Boil some water and pour it inside the bottle, filling the bottle to the top. This will warm up the stainless steel inner walls of the bottle.

Then boil some more water and quickly tip out the current hot water in your Hydro Flask and replace with boiling water. Because the walls are already warm the new boiling water won't cool down as fast.

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What Happens When You Put Boiling Water In a Hydro Flask?

When you put boiling water in a Hydro Flask it instantly starts to cool down. However, the vacuum insulation between the inner and outer wall traps the majority of heat from escaping from the inside of the bottle. This keeps the boiling water hot for 6-12 hours.

I wrote a full article on how Hydro Flask bottles work to keep things hot if you're interested in learning more.

How To Keep Water Boiling For Longer In a Hydro Flask

There are a few different things you can do to keep water (almost) boiling hot for longer in your Hydro Flask and to stop it from cooling down as quickly so you have hot water when you need it.

I wrote a full article on how to keep drinks hotter for longer in your Hydro Flask so read that to see the full details, but here is the shortlist:

  • Pre-heat the inside of the bottle
  • Use a larger quantity of boiling water (the more the better)
  • Use a standard mouth bottle instead of a wide mouth bottle
  • Use an insulating pouch
  • The hotter the starting water the better
  • Keep the lid closed
  • Keep it out of cold environments

Can You Boil Water Inside a Hydro Flask?

It is not advised to actively boil water inside a Hydro Flask and under no circumstances should you put a Hydro Flask on a hot stove or hot element to try and boil the water inside it.

The water wouldn't even boil for a longer time. The heat from the stove would heat the outside metal of the Hydro Flask but due to the insulating properties of the bottle the water inside would not feel much of that heat.

Heating the outside that much would likely cause damage to the vacuum seal, letting air into the vacuum between the inner and outer wall and breaking your Hydro Flask so it no longer insulates properly.

Heating up the outside of your Hydro Flask on a gas or electric stove would also likely do damage to the paint significantly.

Below you can see a video of someone using a vacuum insulated titanium mug and using it to boil water and it absolutely ruins the mug and causes it to deform.

If you wanted to boil water inside a Hydro Flask then I would recommend a hot element you can place inside the bottle to boil the water from the inside, rather than trying to boil it from the outside through the insulation.