Project Harmless borrowed a 1920s pill-coating trick to make poo bags dissolve in water

Walking his four-year-old Swiss Shepherd at Loch Long in Argyll, Edinburgh product designer George Greer was shocked by the plastic dog-waste bags washed up on the shore. Days later, taking a dissolving headache pill, he wondered whether the pill's coating material could be turned into a poo bag. The material had been invented in the 1920s; he tracked down a manufacturer in China and asked his friend Ka Ho Wong, an archaeologist who speaks Cantonese, to liaise with the supplier. Twelve months later the prototypes existed, and the two started Project Harmless.

The bags are water-reactive rather than water-resistant, non-toxic and microplastic-free. The liquid in poo alone degrades their structural integrity, they disintegrate if they end up in rivers or the sea, and after about six days in a bin they start to break down — yet they hold together long enough to do their job. Warm water dissolves them faster, though flushing is not recommended because they stay intact for several days in cold water.

They sell at £15.50 per hundred against roughly £1.50 for supermarket bags whose 'degradable' promise takes about 500 years, by Greer's account. Since selling began on the website in April, Project Harmless has partnered with the Edinburgh Dog and Cat Home and American Express and worked with big department stores in England; environmental activist Laura Young, after looking into the product, called them the most sustainable bags on the market, arguing rival biodegradable and compostable bags rarely encounter the specific conditions they need to break down as intended.

The one disposable bag that never needs to survive water: borrow the dissolving coating from headache pills and make the bag water-reactive, not water-resistant.

Poo bags are the one plastic film that cannot be recycled, so there is no downside to designing it to disappear.

The payload is wet, so water-reactivity attacks nothing the bag actually needs to do.

'Biodegradable' and 'compostable' rivals depend on light, oxygen, heat or nitrogen that landfill never offers, so they persist and emit methane.

A century-old, already-manufactured pill coating removed the need to invent a new material from scratch.

Match a material's weakness to the one job where it doesn't matter. A bag that fails in water is a defect everywhere except the one bag whose contents are wet and which no one can recycle anyway.

Greer quit his job as a product designer to run Project Harmless. By December 2022 the bags were sold through the company's website, with partnerships including the Edinburgh Dog and Cat Home — which called it 'a wonderful Scottish innovation' — and American Express, plus work with large department stores in England.