Bulk Fill Versus Foil – Suspended floor insulation

The September technical update from BRANZ has highlighted the difference in performance of bulk and foil insulation.

By bulk insulation, this is insulation such as glass or mineral fiber, and rigid PIR and extruded polystyrene (XPS) insulation which works by having material R value to resist the transfer of heat.

BRANZ recommends bulk insulation material is used for suspended floors for the following reasons:

  • Bulk insulation provides better performance over a longer period of time.
  • The performance of the foil depends on having a still air space between it and the floor and the foil remaining shiny and intact. Both of these are difficult to achieve on-site and in service.

 BRANZ also highlights that foil loses performance over time,

  • as the surface tarnishes
  • if dust builds up on the surface
  • where wind flows through the gap between the foil and the flooring, as an airtight seal is difficult to achieve at the end of each draped section
  • if damaged by wind.

 For more information please see the Sept 2015 edition of GUIDELINE downloadable from

Andy Russell

Product & Business Development