Insulator for Capacitor

[tomand]

I have a question regarding capacitors in general.
Theoretically a capacitor consists of two metal plates in parallell. In the ideal case where there is vaccum between the plates there should be infinite resistance between the two plate.

I am trying to make a capacitor with two aluminium foil and a plastic foil between them. While checking for a possible short circuit I discovered that there is about 20MOHM or more between the plates.

Is this a short circuit or is the resistance of the plastic foil?

any idea about a better insulator? What is the resistivity of kitchen plastic foil?

Thanks
Tom

 

[alehman]

If thats 20 Megaohms, it is not a short but either conductivity of the plastic, contamination or minor imperfections in the plastic. Commercial capacitors are made with very high grade dielectric materials. It is not surprising to see some leakage with kitchen pastic wrap.

Plasic "Saran" wrap is made of polyvinylidene chloride. I wasn't able to find electrical resisitivity data in a few minutes of googling. You might have better luck.

Mylar is a very good insulator and commonly used in capacitors. It is made from polyester.