most stainless steel or plastic bottles sweat when filled with cold and iced water or other beverages. But do Hydro Flask bottle sweat and if not, why don't they sweat?
Hydro Flask bottles don't sweat when filled with cold or hot drinks except for at the very top of the bottle near the opening.
Most bottles sweat because the drink inside the bottle makes the outside of the bottle colder than the surrounding air. Condensation then occurs where the water particles in the air turn into liquid water on your bottle.
Because Hydro Flask bottles have a vacuum seal the outside doesn't get cold but stays at room temperature and thus doesn't cause condensation or sweating.
Why Don't Hydro Flask Bottles Sweat?
As mentioned above “sweating” (more commonly known as condensation) occurs when the cold outside of the bottle comes in contact with the warm moisture in the air. This causes the moisture in the air to change from a gas into a liquid and sticks to the outside of your bottle.
Over time these drops of water build up and your bottle becomes wet to touch and can even start dripping onto the floor or table.
In regular stainless steel, plastic or glass water bottles the cold ice and drink in your bottle can easily take heat out of the walls of your bottle making it cold and thus causing the sweating to occur.
However, Hydro Flask bottles are made of double walled stainless steel with vacuum insulation.
What this means is that there is an inner and out wall of the bottle, and in between these two walls is a complete vacuum with nothing.
This means the inside metal of your Hydro Flask will get cold to touch, but because it has a vacuum between it and the outer wall it can't draw heat from the outer wall.
Therefore the outer wall stays at room temperature and isn't affected by whatever is in your bottle. Because the outer wall is the same temperature as the air (it's not colder than the air) it won't cause sweating (or condensation) to occur.
Why Does The Top of a Hydro Flask Sweat?
A Hydro Flask bottle DOES sweat a little bit at the top of the bottle near the lid. Why does the bottle sweat here and nowhere else?
The reason this happens is that the bottle is double walled and separated by a vacuum everywhere except the top of the bottle where the inner and outer wall of the bottle connect together.
Your cold drink will cool down the metal on the inside of your bottle. This will draw heat from the metal around it and touching it. Because the metal at the top of the bottle is touching (there is no vacuum between them) this will get cold on both the inside and outside and cause water to condensate and your bottle to sweat.
Stainless steel is actually bad at conducting heat so this effect doesn't continue down the outside of your bottle.
My Own Test
I own 2 Hydro Flask myself and I am very familiar with how they don't sweat except for at the top.
But I wanted to run an experiment so we can see clearly that this is the case.
To test this out I filled up 4 different bottles to the top with ice and cold water and left them to see if they would sweat.
- Hydro Flask 18 oz Standard Mouth Bottle
- Generic insulated stainless steel bottle
- Non-Insulated Stainless Steel Bottle
- Glass Bottle
Very quickly, within a minute, the glass and the non-insulated stainless steel bottle started to sweat and get wet on the outside.
But throughout the entire test neither the Hydro Flask nor the other insulated bottle sweated on the main exterior of the bottle.
The Hydro Flask bottle did sweat a little bit at the top but it was not enough to drip onto the table and make it wet.
In fact, I used my infrared thermometer and could see that the outside of the non-insulated stainless steel bottle and the plastic bottle was close to that of the cold drinks on the inside.
I could also see that the top of the Hydro Flask bottle was colder than the rest of the outside, which remained around room temperature.
Why Do Regular Bottles Sweat?
Regular bottles sweat because of condensation. You likely learned about this in school but totally fine if you’ve forgotten how this works (I did) so let me explain it.
Warm air (whether it be outside or inside) is full of water in the form of gas. When that gas comes in contact with a cold bottle or cup or any surface it turns from gas into a liquid and sticks to your cup.
It’s like your cup is acting as a mini-fridge and turning the warm gas H2O into cold liquid H20.
Without a double wall or any insulation the outside of any regular bottles will always decrease in temperature when filled with a cold beverage, thus causing condensation to happen.
What Can Cause a Hydro Flask To Sweat?
While it's extremely unlikely for your Hydro Flask to sweat anywhere except the very top, there are some circumstances that can cause them to sweat.
It's Lost It's Insulating Ability
This is rare but it does happen. Sometimes Hydro Flasks lose their ability to insulate because there is a compromise in the vacuum seal and the space between the inner and outer walls fills up with air.
Air allows heat transfer much better than a vacuum so if this happens your bottle will no longer keep drinks cold or hot and it also means the outside of your bottle will get cold from the drinks inside and this will cause it to sweat.
Your Hydro Flask Has Been In The Fridge/Freezer
If you've put your Hydro Flask in the fridge or freezer then this will make the outside of your bottle cold.
Once you take it out of the fridge/freezer and bring it into the warmer air it will likely form condensation and sweat for a little bit until the outside warms up to room temperature.
This has nothing to do with the temperature of the drink inside your bottle, but rather the outside is already cold because it's been in a cold place.
While the outside will warm up quite quickly your drink should still stay cold for hours
Time To Upgrade Your Hydro Flask?
Hydro Flask are constantly coming out with new sizes, new colors and different options.
I currently own 2 Hydro Flasks (one for me and one for my kids) but my kids want a bigger one for school so I'll likely be buying another one pretty soon.
If you're interested in getting a Hydro Flask or upgrading yours click the link below:
Taking Care of Your Hydro Flask
Sweating isn't the only thing to think about when it comes to using and taking care of a Hydro Flask. Below are some articles that can help you use your Hydro Flask better: