A well-insulated structure is easier to heat, which allows the radiant designer more flexibility when it comes to choosing floor coverings and radiant system types.
Between-floor insulation in a radiant floor heating system makes the system much easier to control and assures the heat travels where you want it to - upward through the floor, not down through the ceiling to the space below. Under more insulating floors, higher levels of insulation are recommended to prevent this downward heat loss.