This recent article has some careful measurements confirming many of the things we already know about building robust connectivity into e-textiles:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5419786/
They explore the use of TPU and Silicone (NB: they annoyingly misspell Silicone in many places as “silicon”). These are valuable materials for their primary concern (robustness after washing). Their value is also well known for biocompatibility and microbe management and the ones my research for the WearSustain project favored. Another valuable material in terms of inertness and robustness is PTFE (Teflon) which is a common choice for wire insulation where high temperatures are expected. Teflon is not easy to use as a coating or to make enclosure or protective layers. The rather common wire insulation material is PVC which is not recommended for environmental sustainability reasons.
The article also compares several thread choices. The most robust seems to be silver-plated polyamide which even does well when not protected by TPU or Silicone. This concords with our experience and some earlier papers that test the washability of e-textiles. This suggests the the TPU-covered silver-thread from Statex is a very strong candidate for our kit.
The article notes that failures and increases in resistance are often caused by the connection of the threads. We don’t yet have a robust practice or manufacturable process to recommend for attaching Statex TPU thread to our boards and sensors.
Articles on exotic materials to replace our metallic based-threads are appearing. It may take a decade before these are commercially available: https://www.ncbi.nlm.nih.gov/pubmed/29582649