A GLT reader posed some interesting questions recently about disposable paper cups made from post-consumer paper waste.

“Also, is that still more “green” than using reusable plastic cups considering the water and energy used to clean them?,” he asked.

I really didn’t know – the fact the comparison was with a cup made with post-consumer waste was a curve ball; so a little research was involved (spoiler: even after digging around it was still unclear).

According to a 1994 analysis from the Institute For Lifecycle Energy Analysis; with regard to energy savings, “the choice between reusable and disposable cups doesn’t matter much in its overall environmental impact”.

A study quoted by the Institute shows a reusable plastic cup needs to be used around 17 times before it hits the break-even point with a paper cup in terms of energy. So I guess it’s down to how often you used them – I’d certainly get at least 17 uses out of one. Also, with the analysis being nearly 20 years old, it doesn’t take into account the improvements in energy efficiency of dishwashers.

A more recent set of calculations by Jason Munster shows a reusable plastic cup needs to be used around 10 times to hit the energy break-even point; not including any energy involved with washing.

Again, bear in mind the disposable paper cups the reader was referring to are made from post consumer waste.

In my article on recycling energy savings, I mention recycling paper uses about 60% less energy than making paper from new materials – so let’s assume the sort of figure applies with regard to this product. Now the plastic cup needs to be reused around 27 times to hit the break-even point based on the 1994 study.

The number of times a plastic cup will take to hit that point may vary on usage too – for example, I don’t wash my coffee cup after each use (black coffee drinker); therefore my plastic cups hit the break- even point much earlier.

So that’s the energy side of things – but how about water? That was even harder to try and pin down. I wasn’t able to find any direct comparison, but according to this National Geographic page, it takes around 140,000 gallons of water to make a ton of plastic and 54,000 gallons to make a ton of paper.

Given the water savings involved with recycled paper (about 7,000 gallons less per ton); that would put a plastic cup with around 3 times the water footprint of a disposable post-consumer waste based paper cup – but that’s really a guesstimate as other production processes are involved.

Add to that the water used to wash a reusable cup – again, it depends on use. When I wash my cups, I don’t fill up a sink full of water exclusively for that task; it goes in with the day’s other dishes.

This complex story doesn’t end there.

While paper is recyclable, many paper cups are coated with plastic, which makes them difficult to recycle – so they ultimately wind up in landfill.

In a landfill scenario, the paper takes a long time to break down and given the low oxygen environment; methane is produced, which is a powerful greenhouse gas. So really, a disposable paper cup isn’t just made from a renewable resource; it’s also part petroleum product like its full plastic counterpart – and all the issues that accompany plastics apply.

It’s really difficult to arrive at a clear answer to the reader’s question and no doubt I’ve missed out on some aspects – but assuming a reusable plastic cup is of reasonably quality and made from recyclable plastic; I think it would be the “green” winner of the two.

If the comparison was between paper cups made from new materials and reusable recyclable plastic cups – then I think the plastic cup wins hands down as additional factors come into play.