Elias stretch is an origami manoeuvre that is often used while collapsing origami models based on the Box pleating technique. It was named after Neal Elias, who popularized it in the 1970s. The technique is very simple and is used to assemble flaps (polygons) located on the paper edge. Basically, wherever you have a polygon that forms a flap and it is located on the paper edge, you can use Elias stretch manoeuvre to collapse that polygon.