There is a reason for the mechanism of detecting the touch of "CAPTIVATE-METAL". By using electrodes and spacers to create a capacitor directly in the touch area, it is possible to read the change in capacitance caused by the physical shape change due to the pressure applied to the touch area. Therefore, even if you touch it with a non-conductive material, it can be detected.

There is also a video explanation on the Texas Instruments site, so please take a look if you like.
http://www.ti.com/tool/captivate-metal