Fold over elastic (as its mum would call it, FOE is its street name) is thin, flat elastic that has a line running along the centre of its length that makes it easy to fold in half. Sold by the metre, it can be bought in a variety of width and textures, but commonly it is about 20mm when flat and has one matt and one shiny side. Its purpose is similar to bias binding in that it finishes raw edges, but has the added benefit of stretchiness and recovery.