If you need to know more than is in this video, you will probably be interested in everything tagged "theo jansen". Just click it. Yo know you want to!
This shows the raw material that is so ubiquitous in The Netherlands. The PVC electrical duct. This sample is 3/4 inch (yes, that's how it is often called here!) or 19 mm OD. There is a second size widely available that fits exactly inside this one: 5/8 inch or 16 mm.
Note how close Gakken came to matching the colour!https://www.youtube.com/watch?v=xjOJPBDwyxM