Question

What is the best dielectric?

Answer 1

1. Dielectrics: These are materials that prevent current from flowing through them. As they are the polar opposite of conductors, they are more commonly referred to as insulators. When we refer to insulators as "dielectrics," it's normally to emphasize a unique trait that all insulators share polarizability.
2. A perfect vacuum is considered to be the best dielectric. It has a dielectric strength of about $1\times {10}^{12}MV/m$. In reality, it is not possible to create a perfect vacuum so a large vacuum can also be considered a perfect insulator.
3. Apart from that glass, porcelain and silicon are considered to be good dielectrics.
4. A perfect vacuum has the highest strength, rated at $1\times {10}^{12}MV/m$.