Sustainable finance is all the rage these days. What better way to market your green credentials directly to the public than through environmentally-sound credit cards? Many sustainable offerings, however, should be viewed under a microscope to test their claims.

Most people have them. An estimated six billion credit cards are made every year worldwide. But instead of carrying plastic in your wallet, why not have wood or…wait for it…corn.

Zurich Cantonal Bank has teamed up with the company Swiss Wood Solutions to produce an array of biodegradable cards made from sustainable timber. This perfectly taps into the growing demand for designer credit cards that get flashed around restaurants as status symbols. So people can appear unique and chic and climate conscious at the same time. Wow!

UBS is also taking on the neo-banks with their fancy credit card designs. This week, the bank announced a new card made from animal feed corn, which is fermented into a polylactic acid (PLA) material that substitutes for plastic. UBS claims these cards are “more than 80% biodegradable”.

PLA sounds like a wonder material, but some quick research throws up a couple of environmental issues. Firstly, a lot of PLA seems to be manufactured from genetically modified crops. And you can’t just throw PLA on a landfill site and hope it breaks down nicely – it’s only biodegradable under the right conditions.

UBS says its PLA cards are not made from GM crops. Rather than cut up expired cards and throw them in the trash, customers will be invited to return them to a bank branch for disposal. Burning PLA, says the bank, emits far fewer toxic fumes than normal plastic.

Even wooden cards don’t tick all the right environmental boxes, according to the Zurich-based MyClimate Foundation. They told Swiss public broadcaster SRF (in German) that the wooden cards have a similar carbon footprint to plastic because of the energy intensive way they are made.

Swiss Wood Solutions suggests this problem could be alleviated by new manufacturing techniques once production ramps up.

Regardless of the pros and cons of PLA or wood, another answer might be to have a card that doesn’t exist in physical form. This is another product that UBS is launching – a virtual debit card linked to several digital payment platforms. No disposal or recycling problems.

This is all reminiscent of the coffee pod recycling debate that has been running for many years. It’s now the turn of banks to fall over themselves to show they have a social conscience and are good for the planet (the jury is still out on some claims).

Visa and Mastercard have already launched initiatives to improve the sustainability of their cards by using different materials. Environmental NGOs give the unappetizing message that the fish you just bought by credit card may have eaten microplastics from the decomposed remains of other cards – an unpalatable form of recycling.

“How green is your credit card” could be a slogan for the new era of sustainable finance.