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We cut open a Thermik tumbler to let out the science of copper

by Ryley Lyon May 12, 2016

With tumblers finally back in stock, we thought it might be a good idea to slice one up and address a common question we get. Last year, someone posted a video on Youtube of cutting open a Yeti tumbler to find out how it works so well, which has gotten over 50,000 views at the time of writing. What they found was a layer of copper plating inside. So the common question we get is "do Thermik tumblers have copper inside too". The answer to which is yes. But the uncommon question we get is "why". Copper is one of the best heat conductors on earth, so why would we use it?


Inside a Thermik tumbler

The inner layer of a Thermik insulated tumbler.


Let's dive into the physics inside the Thermik vacuum tumbler. There are three ways thermal energy can transfer, making your cold drink warm or your hot drink cool. They are conduction, convection, and radiation. Conduction is heat transfer between two materials that are in contact with each other, for example your tumbler and the hot cupholder in your car. Double stainless steel walls in the Thermik tumbler put a layer of space between the environment and your beverage, taking conduction out of the equation.

The next way is convection, which is energy transfer from motion of a fluid, like air. In our example, this would be warm outside air swirling around, and transferring it's heat to your cool drink. The evacuated chamber inside the Thermik tumbler makes this impossible, since their are no air currents in a vacuum. At this point you might be thinking that an insulated tumbler should keep ice forever, but there is one more avenue for heat transfer that is less obvious.


Copper plating on solar panels

Polished copper solar panels are the only way to capture the sun's energy in space (source:


The third and final way is radiation, which brings us to the importance of the copper layer. Radiation is heat transfer through electromagnetic waves more commonly known as light. But copper is an excellent thermal conductor, so why would it be used in a device meant to insulate? The answer is reflectivity. At normal temperatures on earth, thermal energy radiates in the infrared spectrum, where copper is an excellent reflector. As the outer layer of a Thermik tumbler warms up, it radiates energy towards the inside, even through the vacuum. The copper layer reflects these waves back towards the outside, helping to keep your beverage cool all day long.

Ryley - Co-Founder

Ryley Lyon
Ryley Lyon


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