Why are we protected from lightning sitting in our cars?

A bolt of lightning is a very short duration AC discharge of a
very high voltage.

There have been many reasons postulated as to why
we are safe during a lightning storm inside our cars. One of them is that the rubber tires of
cars is a very good insulator. The second is that the metallic body of the car is equivalent to a
Faraday Cage which limits the current to outside it. The reasons mentioned though are not
accurate. First, rubber is an electrical insulator, but a lightning bolt that has travelled
through several kilometers of air which is a better insulator than rubber is not going to be
stopped by a few centimeters of rubber. Second, the phenomenon of the Faraday Cage is for static
electricity, not AC that makes up a lightning bolt.

The right reason
why we are safe from a lightning strike if we are in our cars during a lightning storm is the
fact that as lightning has a very high frequency it travels only through a very thin outer layer
of the metallic body of the car. This is called the skin effect.

It
is the Skin Effect that protects us if we are seated in a car which has a body made completely of
metal.