Induction: Polarisation

In case of insulators it is a bit different. There electrons cannot move freely through the object. still you can make an air balloon stick to the ceiling, if you have rubbed it against your hair before. The wall was not charged before and cannot conduct electrons either, nevertheless ther is a positive charge in opposition to the negatively charged balloon.

This is because the atoms of the wall aligned with the external charge. Because of polarisation The atoms turned in a way that the negative charge is oriented away from the air balloon. This special case of induction only occurs in case of insulators.