Why is a pipe with 11.6 mm diameter used in the naturbo therm wall heating panel?

An 11.6 mm pipe is used in the naturbo therm wall heating panel to prevent the 31 mm thick naturbo board from becoming even thicker and heavier. However, this does not have any negative effects on the flow rate or the heat output of the naturbo board heating. A 16 mm aluminium composite pipe is used for the flow and return pipes between the heating circuit distributor and the wall or ceiling heating.