Loft insulation uses things like fiberglass to reduce the rate of energy transfer through the roof. The air between the fibers helps with this, and this is why fiberglass is so frequently used.
Cavity Wall insulation reduces the amount of heat lost through the walls of a building. It is put between a inner and outer wall of a building and it traps the air in small bubbles, which is better than just air.
Use the aluminum foil between the radiator and the wall to reflect the radiation away from wall, keeping the heat in.