# What's this substance looking like glass cloth in an electrolytic cap?

This epic image of a blown electrolytic cap is from this question.

It looks like the cap is made of something that looks like glass fiber cloth inside.

What is that material that the inside of the cap is made of?

C = $\frac{\epsilon_r \epsilon_0 A}{t}$ where t is the thickness of the oxide layer, A is the total area of the plates and $\epsilon_r$ and $\epsilon_0$ are the relative permittivity of the oxide and the permittivity of free space respectively.