Heat loss through an uninsulated floor can be as high as 15%. Furthermore, some floors are draughty and insulation can seal the draughts. As the majority of energy lost through the floor is radiant energy, it is preferable to incorporate a reflective layer in the insulation.
The type of floor affects the choice of insulation for subfloor.
Timber floors require insulation that allows ventilation, to prevent moisture build up and subsequent cupping of floor boards. Insulation such as Kingspan AIR-cell Permifloor, are made specifically to allow ventillation of the insulation space. Standard batts also allow ventillation.
Particle board does not have the same problem and any material can be used.