The usual district heating pipes around here have an inner pipe where the actual hot water is pumped, then about 10cm of some yellowish insulation material (pol

The usual district heating pipes around here have an inner pipe where the actual hot water is pumped, then about 10cm of some yellowish insulation material (polyurethane?), and then an outer pipe to protect the insulation. AFAIU heat losses through the piping aren't considered a huge problem.