De la Roy crafted airpop (polystyrene) moulds for the sides of the Zweth eco aquaduct. These moulds had the name ‘Slinksloot’ milled into them. The Zweth eco aquaduct is a combination of an ecoduct and an aquaduct. It is located near Schiedam in the Netherlands, and is part of the A4 motorway running between Delft and Rotterdam.