Folks living in tempeterate climate do not understand insulating at all.
Heat escapes via surface which has less insulation. It does not help if you insulate 5 side of cubic if the sixth lead the heat out.
Moisture condensates to the coldest surface. The inner roof must have good insulation that condensation happens onto side walls.
The heat conducts via material, not cold. If you have a double wall and only air between them, it is like a double window. It cuts the heat conduction and air is the best insulation. Loose material in air gap stops the air circulation and heat movement with air.
How many of you use douple window in houses? We use to have here 3 glasses when we spare energy.