also see: Materials >> Conductive Threads
You can’t solder to most conductive threads, but there are conductive threads that are actually made by spinning very thin flattened wire around a soft, flexible core, and these are great for soldering to.

also see: Materials >> Conductive Fabrics
Of the conductive fabrics I tried soldering to, only the copper FlecTron fabric distributed by LessEMF was very reliable. There was another silver fabric that worked, but I don’t know the source. The Laird conductive fabric tape was also good, so were copper mesh and copper foil tape with conductive [...]

I had hard time soldering DIP pin legs to conductive fabric. It becomes always crumbly and does not stick to the fabric good. (Also I am using lead free solder, that makes it look crumbly too)

Acrylic board with holes drilled every 4mm spacing for electronic components. this is also about the minimum distance for spacing when sewing with conductive thread. Perfboards with copper line patterns are great for making small circuits and then sewing to them (by hand) with thread that is not too thick and does not fray too [...]