Practical  capacitors:

It is out of the question to make a capacitor of above dimensions. But two sheets, or strips, of the foil can be placed one on top of another, separated by a thin, non conducting sheet like paper, and then whole assembly can be rolled up to obtain a large effective surface area. When this is done, electric flux becomes great enough so that the device exhibits significant capacitance.  Actually two sets of several plates each can be meshed, with air in between them, and the resulting capacitance will be significant at high alternating current frequencies.

In a capacitor, the electric flux concentration is multiplied when the dielectric of a certain type which is placed between the plates. Plastics work good for this purpose. This increases effective surface area of plates, so that a physically small component can be made to have large capacitance.

The voltage which a capacitor can handle depends on thickness of the metal sheets or strips, on spacing between them, and on type of dielectric used.

Generally, capacitance is proportional to the surface area of the conducting plates or sheets. Capacitance is no directly proportional to the separation between conducting sheets; or we can say that the closer the sheets are to each other, the greater the capacitance. The capacitance depends on the dielectric constant of the material between plates. A vacuum has a dielectric constant of 1; some substances have dielectric constants which multiply the effective capacitance many times.