The commercial flexible resistors are very expensive. Making a whole glove out of them was not reasonable. Also, in testing, I was not impressed with their sensitivity. I looking into making my own and found some good resources. I am using this method with some modifications:

I am using Velostat from adafruit. 3 layers works well. I have substituted the conductive thread for wire-wrapping wire. It is flexible as well and allows me to attach the other end of the wire to a header pin easily (with a wire-wrapping tool). I am also using electrical tape instead of duct tape. I don't think that has any effect.

I may experiment further with using conductive foils to increase the sensitive area. This design above appears to rely on the wires and layers being pressed together. If the wire is not pressed on, the resistance may not change much. This is not an issue in the glove as I simply situate the wire over the knuckle, but a better version would be appreciated.