Last year, some 100,000 tonnes of polyethylene terephthalate (PET) were recycled in Taiwan. That represents roughly 80 per cent of the country’s total production of the material, which is used mainly for making plastic bottles. The inventors of the “polli bricks”, as they are known, had the idea of creating a building material also in the form of a bottle and consisting to 100 per cent of PET. These units, with a capacity of roughly two litres of liquid, engage firmly with adjoining units, nevertheless leaving interstices that improve sound and thermal insulation (U = 1.5 W/m2K).