Coffee cup calculus

Note: The post below is reprinted as it appeared in the University Observer (online here and in the physical edition).

Nothing epitomises our throwaway culture quite like the coffee cup. Paper cups cannot be recycled because they are lined with a thin layer of plastic which cannot be separated from the paper. Hence, two million cups end up in Irish landfills each year.

UCD are accountable for thousands of these cups and the Students’ Union has acted in response to this, with SU shops offering a €0.20 discount on tea or coffee when a reusable cup is used instead of the standard disposable cup. Branded mugs can be bought in the Student Union shops for €5.00 and the first cup of your beverage of choice is then free. Such a discount scheme is compelling, even if it takes 20 uses before one profits from the exchange. However, since the key motivation is to reduce the environmental impact, the central issue is the number of times the reusable mug must be used before it becomes the most eco-friendly choice. A life-cycle assessment is required to compare reusable cups to their disposable counterparts.

Source: Vegware

First we must look at the manufacturing process. Due to their durability, making reusable cups is far more intensive, requiring multiple materials. On top of this, the cups are often sold with excessive packaging. Paper cups require far less energy. However, very little recycled paper is used in these cups, and it is estimated that a tree is cut down for every 2,500 cups produced. As well as the loss of potential natural habitat that comes with removing these trees from the ecosystem, there is also the loss of the ability to absorb carbon dioxide.

Both products must then be transported to the stores. A cup that is made locally will have less of an impact than a cup that is shipped thousands of kilometres. Although both paper and reusable cups are subject to the same transport conditions, paper cups can be packed more densely, thereby reducing the transportation impact. The fact that reusable cups are heavier also impacts the fuel usage required to transport them.

The environmental effect of cleaning reusable cups is often overlooked, and using a dishwasher to wash the cup significantly increases the CO2 emissions and the energy usage of the cup. Studies have shown handwashing to be significantly more efficient. As paper cups are single-use, there is no associated impact from having to clean them.

The most crucial variable of the equation is the disposal of the cups. The non-recyclability of disposable cups means that they either wind up in a landfill or in an incinerator. Each option has its drawbacks. Older incinerators merely burned the waste, whereas newer plants, such as the Poolbeg incinerator, also harness this heat to generate electric power. However, incinerating a paper cup recoups a negligible amount of energy while simultaneously releasing a sizeable amount of CO2 into the atmosphere. If they instead go to landfill, though, they can take a long time to disintegrate, potentially becoming a pollutant and being ingested by marine life.

The end-of-life treatment of reusable mugs cannot be neglected. Due to the robust materials from which they are made they are likely to take hundreds of years to decompose in a landfill, while contributing to the pollution associated with landfill usage.

Without information as to where the UCDSU cup was manufactured, what materials were used, and the product’s lifespan, it is difficult to say how it measures up against the paper cup in each domain.

Several studies have addressed this issue using similar reusable cups where the global warming potential and the non-renewable energy usage are used to quantify the differences between reusable and disposable cups. There is broad consensus in the results: A reusable cup, whether it is plastic, ceramic, or glass, must be used between ten and twenty times before it becomes more environmental than a standard paper cup.

All reusable cups are not created equally, however, and there are several reusable cups which are particularly considerate from an environmental standpoint, namely the Ecoffee Cup (which is made from bamboo fibre) and the KeepCup.


This is a KeepCup. Many companies are selling branded versions of this cup.

In terms of disposable cups, polystyrene cups actually have a lower carbon footprint than the paper alternative, although they present a more significant pollution threat. The ideal scenario would involve a shift from a linear economy to a circular economy in which resources and waste are minimised and disposable cups are manufactured from recycled material with a high recovery rate.

Comparisons of the life-cycle assessments of reusable versus disposable cups, while far from a precise science, tend to reach similar conclusions. Short of curtailing our tea and coffee intake, reusable mugs are the best option, and its impact is reduced considerably when hand-washed. If you must use a paper cup, avoid a lid unless necessary. In any case, buying a reusable mug only for it to get lost at the bottom of a bag after a handful of uses is the worst outcome.

Finally, we should be cognisant of which tea or coffee actually goes into the cup, prioritising brands which take their social and environmental responsibilities seriously. Buying coffee is not exactly a piece of cake.