Following the same principal that you’ll find inside a traditional round and slider potentiometers. Both contain a wiper finger (conductive) and a resistive track. Normally both ends of the restive track end in separate measuring point tabs, as does the wiper finger. Thus you can choose to measure from either of the restive track tabs and the wiper finger, and you will be able to adjust the resistance by turning or sliding the potentiometer.

The fabric version of this principal uses EeonTex piezo-resistive SL-PA coated fabric RL-4-139-4 from Eeonyx but you can also use resistive thread from LessEMF for the resistive track and a piece of wire, a metal bead, ball or conductive fabric, for the conductive wiper finger. In these examples only one end of the resistive track is connected to a measuring point and the other measuring point is the wiper finger.

Time Sensing Bracelet

The circular fabric potentiometer is used in the Time Sensing Bracelet, a funky demonstration of how it works. The first version used a conductive fingertip to make the connection between the conductive fabric circle in the center and the restive track. A second version made use of a wire extension of a metal popper that was pieced through the central conductive circle, this could turn around freely, but had to be pressured to the resistive fabric to make good contact.

The Eeonyx fabric is not only resistive over distance, but its resistance is also pressure sensitive. This is great for making pressure sensors, but makes the fabric potentiometer less accurate. Also, the resistance of this particular Eeonyx fabric does not rise linearly over distance. In the example of the Time Sensing Bracelet, this was compensated for in the software.
>> http://www.instructables.com/id/Time_Sensing_Bracelet/

Making Resistors

Syuzi Pakhchyan has published a sewable version of a sliding potentiometer that uses a magnet to keep the “wiping finger” in place. You’ll find the detailed instructions on how to make this in her book Fashioning Technology on page 66 “Making Resistors”.
Fashioning Technology >> http://www.fashioningtechnology.com/

Pictures on Flickr