I am designing a capacitive sensor. Which is based on a capacitive voltage divider. And i have a time constant arround 1000 sec. To increase the time constant of my sensor i am looking for a capacitor. As the insulation resistance of my sensor is arround 1000Tohm. So I am looking for a capacitor of 1000PF and 1000Tohm or with even higher insulation resistance. but I donot really know that which type (ceramic or film) of capacitors have high insulation resistance. As I films like PTFE has high surface resistance arround 10^18 ohm. so I thought that PTFE film capacitors could be the best option. But I could only found capacitor in ther rang of max 10Gohm. Can anybody tell me if someone have some experience using such capacitors. That is it possible to get a capacitor with such high resistance ?