A 25C wash is greenest – but can it really clean filthy clothes?

Clothes washed at 25C on a 30-minute cycle shed fewer microfibres into waste water and keep their colour for longer, researchers at the University of Leeds have found. This makes sense. After all, consumers have long been advised by detergent manufacturers and environmental organisations to turn down the dial on the washing machine to 30C. Dropping to 25C is a small adjustment, but possibly a greater psychological one: will clothes really be clean at that temperature, and on such a short cycle?

Lucy Cotton, the report’s lead author, explains that 25C is usually the “inlet” temperature of water in a washing machine – the natural, unchilled and unheated temperature at which the water enters the drum. Her research tested the release of dye and of microfibres from a range of consumer clothing, such as Fruit of the Loom Tshirts. However, the clothes were not dirty when they went into the wash, and only the release of microfibres and desorption of dye were measured. “We weren’t testing for cleanliness,” she says. “One of the things that is useful about this study is that it puts the onus on detergent manufacturers to explore this area. Can they make the cleanliness happen in a cold, quick wash?”

Wrap, the waste reduction charity that has a campaign called Love Your Clothes, considers 30C to be a cold wash – even though, in 2013, the EU’s Ecodesign initiative made an even lower 20C setting compulsory on new washing machine models, and 30C is not cold (my local outdoor lido is

heated to 25C). But according to the Energy Savings Trust, washing clothing at 20C instead of 40C saves about 66% of the energy used for a load (compared to a 40% saving for dropping to 30C).

Proctor & Gamble tested its Ariel Gel for effectiveness and stain removal at 20C, while Which? magazine found in a test that an olive oil stain was the only one a 20C wash couldn’t shift compared with a 40C wash. It’s got to be worth a try. But just remember to keep the cycle length short, and avoid a delicates wash because these use more water than average cycles and cause more microfibres to shed.