I'm a bit late on my reply, but the material used by ST was not cardboard. It was a form of coco fibre called coir, made from coconut husks and compressed into boards or sometimes woven into a coarse rope. You will find coir in old furniture and auto upholstery for tacking and also where compressed horsehair had been used. Considering the demise of horse drawn conveyances, and the ample supply of coconuts in the British colonies, it is believed that this material was a lower cost alternative to horse hair products.
BTW, for this application, we used nylon rectangular bar stock which is readily available from suppliers like McMaster Carr. others I know have used natural fibre hemp rope.
T