to one of the shops which sells it.
I found mine in an Art and Craft shop in the beads department.
The purpose was to replace the hinges on the door panes which are to thin for real hinges.
The trick is to set the elastic thread between the two layers of wood,
to do so:
decide where you want to have the thread, groove a line where the thread will go on one layer. Then glue the 2 layers together making sure the groove is still there. Use a thin piece of metal to make sure the gap isn't filled with glue.
If you look carefully you can see the different threads on the picture below
When the glue has set, you should be able to insert the nylon inside the panel and add the different panels.
To insert the nylon string, cover the end with this glue that we call "colle contact" here as it can glue your fingers in 1/2 a second. I don't know what you call it in English. That way, the nylon thread can be easily insert between the 2 layers of wood.
Make a knot on each side if the thread so that the door panes are set together. Now you have an invisible hinge that works pretty well
I am sorry if I am not clear but feel free to ask me any other question about it.
Have a nice day!