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.
In this blog post, I would like to address the problem of unused parts of a paper. This problem is not uncommon in origami. As a matter a fact, you will stumble upon it quite a lot, and in this regard box pleating technique is no exception. Simply, when polygons and rivers are arranged on a square piece of paper, it is very likely that part of a paper will be left unused.