Hi Fin,
The sonic difference between teflon and thread such as cotton or silk has to do with the microphonic resonance, or vibration, of a wire when a signal travels through it. When the wire vibrates, even though its just a little, it will "rattle" more when encased in a hard substance vs a soft substance. Think of shaking a rock in a plastic cup versus a cotton sock. It is especially important before the amplifier, where that rattle will just be amplified.
Now whether or not there is a difference between cotton and silk, I don't know. I doubt if there is. I guess it just depends on whether you are willing to take your cables to the dry cleaners. ;-)
Hope that helps.
Holly