What requirements must a molecule meet in order to be considered nonpolar?

In order for a molecule to be considered non-polar it must be symmetrical and it must not contain a polar bond. The real difference between a polar and non-polar molecule is that the polar molecule has a positive electrical charge on one side and a negative electrical charge on the other side. The non-polar molecule has no separation of electrical charge as they are evenly distributed across the molecule.

The mass has escaped into a gas which you can not see so the law stays true.