Ask Pablo: The Coffee Mug Debacle

Welcome to the first installment of “AskPablo” where you get to ask me your burning sustainability questions like “paper or plastic?” and “driving with the window open or A/C?” I look forward to reading your e-mails and helping you understand the science behind sustainable decision-making. We engineers tend to use a language of our own so I will do my best to translate it to English.
This week’s question comes to us from TriplePundit creator, Nick Aster: “What’s better for my daily coffee in the context of as many different environmental and social impacts you can think of? – an aluminum mug, a ceramic mug, or a new paper cup every day?” To make things a bit more interesting I am going to take some artistic license and change the question to encompass a Stainless Steel Mug, a Ceramic Mug, and a Styrofoam Cup. Since we are such a caffeine fueled society I have chosen to compare each of these at a 16 oz. size.

Stainless Steel (SS) is a ferrous alloy (a combination of two or more elements that includes iron). It contains at least 10% Chromium, which gives it anti-corrosive properties (English: it won’t rust). Each gram of SS is responsible for the use,displacement, or consumption of 14.4g of abiotic material (mineral substances including ore and fossil fuels), 205g of water, and is responsible for the release of 2.8g of greenhouse gasses (GHGs).
Ceramic is an ” inorganic non-metallic materials whose formation is due to the action of heat” (hooray Wikipedia!). Basically it is a clay that requires kiln firing to remove moisture… Since it is made by heating up some dirt it’s impact is relatively minimal. To create one gram of ceramic we inconvenience 2.11g of abiotic material (mostly the clay and some natural gas), 5.3g of water, and we create a mere 0.065g of GHGs.
Our final material for this analysis is polystyrene (”many styrenes”, linked in a long chain), also known by the brand name Styrofoam. Polystyrene (PS) is a thermoplastic (meaning that it can be melted repeatedly, as opposed to a thermoset plastic like epoxy which can not be melted), making it recyclable. Unfortunately it is not recycled in many states, including California. The reason for this can be found in simple economics. Since expanded polystyrene (foam, as opposed to the PS that is found in many clear drinking cups, especially on many airlines) takes up a lot of space, relative to its low weight, it can not be economically transported over long distances to the nearest recycling plant that is capable of processing it. Pre-processing it locally before shipment requires expensive equipment which is not justified by the low value of the recycled material (since it’s just so cheap to make it from scratch). So, to our dismay, most of it ends up in landfills (to be extracted by future generations, right?). To create 1 gram of PS requires the use of 2.51g of abiotic material (mostly the oil from which it is made), 164g of water, and is responsible for the release of 2.8g of GHGs.
Since the PS cup is considered disposable and the other two are intended for daily reuse we are comparing apples to oranges, right? Well, not if we compare them per “service unit.” In this case our service unit is ” the service of holding the caffeinated morning beverage of our choice while we drag ourselves to work.” We have analyzed the materials, now we need to determine the material intensity per unit.
In my research I found the weights of each of the following 16 oz. beverage containers:
Polystyrene – 6g
Ceramic – 322g
Stainless Steel – 378g
Now, by multiplying the material intensity values that we found earlier by each container’s weight, we can find their total material intensity. For each 16 oz. container we use the following amount of abiotic material:
Polystyrene – 14.8g
Ceramic – 679.4g
Stainless Steel – 5454.5g
Based on this result alone, you would have to use your mug at least 46 times (daily for a month and a half) and you would have to use your SS mug at least 369 times (daily for a year) to justify its higher material intensity. The results for water are a little more difficult to grasp since water is a renewable resource that continues through its natural cycles after we use it (PS – 966g, Ceramic – 1,706g, SS – 77,528g). For the highly-processed SS, we need 164 times as much water as the mug holds ( 77.5 liters)!
The results in the GHG category are also quite striking. Keep in mind that, based on UN figures on the cost of climate change and the annual global CO2 emissions, each ton of GHGs is responsible for $8 in damages. (PS – 16.5, Ceramic – 20.9, SS – 1068g) Again, the Stainless Steel has the greatest material intensity with over 1kg of GHGs, or roughly $0.01 in climate change-related damages.
This essentially concludes my analysis. In summary, a ceramic mug has the lowest material intensity of the three as long as you use it at least 46 times. Since most ceramic mugs enjoy long and happy lives in our kitchens this is quite feasible. But please remember that purchasing tacky or holiday-themed mugs that will recieve limited use actually have a higher environmental impact than styrofoam cups do! So, if you don’t already have a reusable beverage container go out and get yourself something timeless and use it often.
I hope that I have helped you understand a little bit of the science behind sustainable decision-making. I welcome you comments and please keep the questions coming. See you next week!