Sitting around in wet swimming trunks is not good for health, hygiene or happiness, but until now, waterproofing coatings for fabrics have been problematic for the environment.

To retain its shape and dry quickly, swimwear must combine two properties: it must be elastic and must not soak-up water. Since the 1970s, synthetic compounds have been used for waterproofing, but washed into the environment via the sewerage network, these per and poly-fluorocarbon chemicals - PFAS for short - accumulate and do not degrade.

Ultimately they can end up in the bodies of humans and wildlife, and PFAS are suspected of causing various health problems including cancer, cardiovascular diseases and developmental disorders. Certain PFAS are already banned, others could follow.

Scientists in Switzerland are now working closely with textile companies to develop innovative processes that can give fibres an environmentally-friendly, water-repellent finish. The researchers at the Empa research institute say an equivalent, or even improved, water-repellent effect can be achieved by treating textiles with organic chemicals called siloxanes.

Dirk Hegemann from Empa's advanced fibres laboratory in St Gallen says the process uses organic compounds called siloxanes, which are cross-linked to form silicone-like layers. Unlike fluorine-containing PFAS, he says, siloxane fibre-coatings are harmless to the environment.

The siloxanes enclose the textile fibres in a water-repellent coating just 30 nanometers thick. They can then be processed into water-repellent textiles of all kinds, including clothing and upholstery fabrics.

The advantage over conventional waterproofing processes is that even with complex structured textiles, distribution of the hydrophobic substance can be delivered into every turns of the intertwined fibres. This is crucial, because even a tiny wettable spot would be enough for water to penetrate into the depths of a pair of swimming trunks, preventing the garment from drying quickly.

"We have even succeeded in permanently impregnating more demanding, elastic fibres with the new process, which was previously not possible," says Hegemann.

Interest from industry

In initial laboratory analyses, textiles made from the new fibres with the environmentally-friendly coating are already performing slightly better than conventional PFAS-coated fabrics. They absorb less water and dry faster.

However, the miraculous properties of the fluorine-free coating only really come into their own after the textiles have been washed several times. The performance of conventional PFAS coatings in stretchy textiles declines considerably after repeated wash cycles, while the fluorine-free fibres retain their water-repellent properties.

Hegemann and his team are now working on scaling-up the fluorine-free process into an economically viable industrial process.

"The industry is very interested in finding sustainable alternatives to PFAS," he says, and Swiss textile companies Lothos KLG, Bäumlin & Ernst and Cilander are already on board.

Dominik Pregger from Lothos says, "This is a successful collaboration that combines materials, fibre technology and plasma coating, and leads to an innovative, sustainable and effective solution."

Bernd Schäfer, chief executive of Bäumlin & Ernst adds, "The technology is environmentally friendly and also has interesting economic potential."