Types Of Underlay

Apart from their fire retardance and ability to self-support, underlays are classified according to their absorbency and permeability.

Permeable and Absorbent:

  • Kraft paper-based — bitumen impregnated paper
  • Synthetic — 2 or 3 layers, using permeable synthetic film strengthened by sandwiched non-woven fabric.

Permeable, non-absorbent:

  • Synthetic permeable non-absorbent underlays are mainly used as wall wrap inside a drained cavity or with direct fixed absorbent claddings.

Non-Permeable, non-absorbent:

  • foil — Reflective aluminium foil over a flexible substrate. These can be either double-sided or white-faced.
Clause Number: 
Revision Category: 
2 - Editing and rearrangement
Revision Detail: 

Clause revised for clarity.

Draft Clause: