Hydro Flask bottles work really well to keep beverages ice cold or super hot for extremely long periods of time. But how exactly do Hydro Flask bottles work? How do they keep things hot and cold?
Hydro Flask bottles are made of vacuum insulated stainless steel. The vacuum (or nothingness) in between the inner and outer walls of the Hydro Flask stops most heat from entering or escaping the bottle. This is how they keep drinks hot/cold for so long.
The inside also has a copper plating to insulate against heat radiation and stainless steel itself is actually a poor conductor of heat so provides some minor insulation.
All of these elements, combined with a thick plastic lid (plastic is also an insulator) all Hydro Flask bottles to keep drinks ice cold for 24+ hours or hot for 12+ hours.
I currently own 2 Hydro Flask bottles (one 18 oz standard mouth bottle for myself and a 12 oz kids bottle that my children like to use).
I have personally experienced how good these bottles are at keeping drinks cold and hot. I also own a bunch of other big-brand insulated bottles like YETI and Klean Kanteen as well as some generic insulated bottles I got from my local supermarket.
In this article we are going to go in depth in exactly how Hydro Flasks keep heat out or keep heat in. It's actually quite fascinating.
Double Walled and Vacuum Sealed
While a Hydro Flask might look like just another painted metal bottle, it's actually got two walls – an inner and outer wall.
There's a gap between this inner and outer wall and inside that gap is vacuum. They suck all the air out so there's basically nothing in there, or as close to nothing as they can get.
It is this vacuum that allows Hydro Flasks to work so well.
How The Hydro Flask Insulates Against The 3 Types of Heat Transfer
See, there's different ways that heat is transferred from the outside air to the inside of your bottle:
1. Conduction (Touching Heat)
Heat can move from one object into another by touching it.
The external heat from the air touches the outside of your bottle and warms up the metal on the outside.
However, because the outside of a Hydro Flask is NOT touching the inside (and there isn't even any air in between to transfer heat) it can't use conduction to transfer heat and warm up your iced water.
The same is true for hot drinks on the inside of your Hydro Flask. The inside wall isn't touching the outside wall so heat can't get out. It's trapped inside.
Stainless steel is also a poor conductor which stops the Hydro Flask bottle from conducting heat easily in the first place.
2. Convection (Moving Heat)
Convection is when heat moves from one spot to another.
For example a hot pocket of water can be pushed through a bath (or bottle) to warm up other areas. The same happens with air.
Again you have a vacuum with no air or water particles so no heat can move around through convection.
The only way convection occurs is when you open the lid of your Hydro Flask to have a drink warm air flows into your bottle and the colder air flows out.
Radiation is heat that can pass through a vacuum (like gamma rays but way way way less dangerous).
The sun's rays obviously travel through space (which is a vacuum) and warm up the Earth. Radiant heat is always happening as will be able to pass through a vacuum.
This is why you should keep your Hydro Flask out of direct sunlight if you want ice to last longer. Click here to learn 8 tips on how to keep ice longer in your Hydro Flask.
So the vacuum of the cup won't protect against this kind of heat. Inside the inside of the bottle is copper plated.
Copper is a great reflector of radiation and so have that copper lining actually reflects the radiation trying to get in.
The Mouth Of The Bottle Lets the Most Heat In/Out
The top of the bottle where the mouth/lid is located is the area that lets the most heat into the bottle or lets the most heat escape from the bottle.
The top of the bottle is where the inner and outer wall come together and are touching, so there's no vacuum there. This can cause the top of your Hydro Flask bottle to sweat.
The lid's are made of plastic and are decent insulators, but they aren't quite as efficient as the vacuum seal.
The Standard Mouth design is smaller and the Standard Mouth lids are thicker and thus they can hold ice for longer than Wide Mouth bottles.
The Lid Also Provides Insulation
Hydro Flask lids are made with thick plastic and have a rubber gasket to make them watertight and airtight.
The plastic is an insulator so it helps to keep heat out of your bottle or keep heat in your bottle.
The rubber gasket stops warm air coming into your bottle and warming up your water.
As mentioned above, Standard Mouth lids are thicker than Wide Mouth lids due to their design and the thread being on the inside of the bottle not the outside.
This means they insulate better than wide mouth bottle lids.
Hydro Flask Vacuum Seals DON'T Use Lead (Other Brands Do)
Something unique about Hydro Flask is the fact that they use a special manufacturing process called “Tempshield” that creates the vacuum seal on their water bottles without the use of any lead.
Other vacuum sealed water bottles use lead welding in order to create the vacuum seal.
Lead is obviously very dangerous and it isn't something I want anywhere near my water bottle so I love that Hydro Flask have done away with this.
Click here to learn whether or not Hydro Flask bottles cause cancer.
Time To Upgrade Your Hydro Flask?
Hydro Flasks are great bottles and they really do work extremely well. I own 2 of them and absolutely love them and my kids love them too.
I'm going to need to upgrade soon because my kids keep stealing mine and I want to get a bigger size anyway.
If you're looking to get your first Hydro Flask or want to upgrade your Hydro Flask bottle then simply click the link below to see the latest prices at Amazon: