What is the functional difference between the longer, harsher outer coat and the undercoat of the German Spitz?

Answer

The outer coat sheds snow and moisture, while the undercoat traps air for warmth

The undercoat is designed to trap air for warmth, while the longer, harsher outer coat serves the purpose of shedding snow and moisture away from the body.

What is the functional difference between the longer, harsher outer coat and the undercoat of the German Spitz?
Dogcoldpetbreedspitz