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Ceramic or Glass Coffee Cups?

Selecting a coffee cup is a very personal choice. While you may have a variety of mugs, you probably have one that you favor above all the rest. Typically, a favorite mug is an aesthetic matter, but there are other factors that can come into play when settling on one go-to cup. If you’re looking for a new favorite coffee mug, here’s a look at glass and ceramic choices from a thermodynamic and environmental point of view.

Ceramic Retains Heat Better Than Glass

As far as keeping your coffee warm goes, ceramic outperforms glass. In addition to heat lost through evaporation, which depends on the mug’s shape and the surface area of the coffee exposed to the air, your coffee will cool off as the mug, itself, draws heat through conduction and loses it through convection. In both of these areas, ceramic loses heat at a slower rate than glass.

Conduction is loss of heat through the direct contact of two materials, one of which is a colder than the other. Because ceramic is more porous than glass, conduction occurs slower in ceramic mugs. The little pockets of air that are trapped inside the ceramic act as insulators and slow the process of conduction.

Convection is the loss of heat through contact with air. Once the mug initially warms up, it will lose heat through convection. In turn, this causes it to draw more heat from the coffee via conduction. Ceramic has a higher specific heat (~900 J/kg.K) than glass (~800 J/kj.K), which means ceramic will lose heat through convection at a slightly slower pace than glass. With a ceramic mug, heat loss through convection should occur about 11.1 percent slower (100 – (800 J/kj.K / 900 J/kj.K)) than it would through a glass mug of the same shape and size.

In short, in case you aren’t a science person, a ceramic mug will keep your coffee a little warmer than a glass one.

Locally Recycled Glass is Most Environmentally Friendly

Deciding whether glass or ceramic has an edge from an environmental point of view is not as straightforward as comparing their heat loss. Both have advantages and disadvantages.

On the one hand, glass can be recycled, but ceramic generally cannot. (Technically, some ceramics can be “downcycled” and incorporated into other ceramic products, but downcycling produces a poor quality ceramic that isn’t typically used in mugs). This gives glass a distinct edge over ceramic in a comparison of their environmental impacts.

On the other hand, ceramic doesn’t weigh as much as class, and, therefore, requires less energy to be shipped. While the difference in weight between one glass mug and one ceramic mug may seem negligible, even a fraction of an ounce adds up when shipping hundreds or thousands of mugs.

The best environmental choice would be to purchase a mug made with glass locally sourced recycled glass. This takes advantage of recycling glass without the tradeoff of using more fuel to ship it long distances. If you can’t find a mug that is made from locally recycled glass, you’ll have to decide whether recycled glass or lighter ceramic is better for the environment.

The next time you come across a mug you like, don’t just think about the aesthetics of a mug. Consider how the mug will impact your coffee drinking and the environment. A mug says a lot about a person. Yours should reflect well on you in all three areas: aesthetics, thermodynamics and environmental impact.

Author Scott

Scott is a professional writer for Driftaway Coffee. He worked as a barista for eight years, but today prefers to enjoy his beverages from the other side of the counter. When not drinking Driftaway Coffee, Scott usually has a mug of his own roasted coffee nearby.

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  • Anisa Trisha

    Hi :) Can I ask about the aluminum or plastic? If what is more recommendable between the two? It has the same situation with the glass and ceramic. Please answer me. Hehe :)

    • https://driftaway.coffee Driftaway Coffee

      Hi! That depends on the type of plastic to be honest. I’d say that in general aluminum is preferred since its reusable, whereas most plastics are not. However there are some exceptions with some plastics.

  • Charlene Yonce

    Is the a difference in taste between ceramic or glass mugs? According to the experts.

  • William

    I disagree!
    The answer depends on the ceramic you choose. Most of the ceramics have low thermal conductivity at room temperature but there are ceramics which have very high thermal conductivity.
    It’s useful to also compare metal cups. Metals have the highest thermal conductivity in general. Ceramics follow metals and then comes glass. Heat transfer from coffee to the air is by convection which remains a constant in all the three cases.
    A metal cup cools fastest. This is because the heat of coffee is conducted to the outer periphery of the cup very fast. Due to this the temperature of the cup is almost same as the temperature of the coffee in it. Heat is transferred by convection to air from the walls of the cup. The metal walls of the cup also radiate heat. In the case of metals all the three modes of heat transfer play a predominant role. So the metal cup cools faster.
    At room temperature most ceramics are insulating and possess thermal conductivities ranging from 3-60 W/m-K. Heat conducted to the outer wall is less than the heat conducted to the wall of a metal cup. Radiation heat loss is less than that of metal as radiation is directly proportional to temperature raised to a power of 4. Due to low thermal conductivity the temperature of the outer wall of ceramic is considerably less than that of a metal cup which implies lower radiation heat loss. Also the convective heat loss is low as the temperature gradient is low.
    In the case of glass cup, the outer wall of the cup is cooler than that of a ceramic cup. The heat flux to the periphery is also low as the thermal conductivity of glass is also lower than that of ceramics.
    This implies that glass cup has the lowest convective and radiation losses from the cup.
    Metal cup cools first followed by ceramics followed by glass.