A rigid printed circuit board is a plate made from composite materials in general of epoxy glass also named FR4 (acronym for flammable resistant 4) plywood with one or more layers of copper. A rigid board has a thickness between 0.2 mm and 4.5 mm and a copper thickness ranging from 17.5 µm to 420 µm.
An aluminum board is made of a metal plate with one or two copper layers, the thickness of the material as well as the copper can vary by project. The main advantage of the aluminum is to dissipate the heat of certain components, especially LEDs.
A flexible board has the physical ability to bend, it is made of polyimide (PI) whose main feature is a high resistance to physical handling and high temperature. It is available from 1 to 12 layers.
A flex-rigid PCB is an assembly of interconnected rigid and flexible parts, it is available from 1 to 30 layers.