Origami boxes and tetrahedron volume

A few days ago I attended a short course on origami boxes. Among the various models I have been hit by Hildegards Schächtele.

Figure 1. Hildegards Schächtele

The diagrams of this easy modular model (two units) are available at the website of the author Carmen Sprung.

The shape of the box is that of an irregular tetrahedron formed by four faces that are congruent isosceles triangles. The opening of the box is an edge.

I wondered if this model had some special mathematical property or some educational interest.

A good exercise for young students consists of calculating the volume of the box given 

1. the length L of the side of the square of the sheet of paper; 
2. the possibility to manipulate the model; 
3. the crease pattern of the model.

Figure 2. Geometry of the crease pattern

The solution of the problem is left to the reader!

Before concluding, it is interesting to note that the problem of calculating the volume of an irregular tetrahedron has very interesting mathematical implications. See here for example.