Alternative to Cloth&Thread
The usage of cloth with sewn thread imposes many problems. It might be a good idea to rethink the usage of this.
We could make a flattened silicone sheet containing a network of stiffer silicone, which would replace the function of the thread. The sheet would be made of the same silicone as the tube, which would meld together when pouring the outer layer. For this to work we need a silicone that is significantly stiffer than the ones we have, but we suspect this is available.