You are here:

Flexible Sponge Cavity Barrier (WBS & VWBS)

Product 55



Flexible, moisture resistant barriers for use in brick wall cavities

Not available to purchase online.

We need to ask you a few more questions and ensure this is the suitable product for your needs.

To order please call us on +44 (0) 1 304 842 555



Flexible Sponge Cavity Barrier

The WBS cavity barrier is a flexible, fireproof sponge fixed in a horizontal or vertical position in a brick/ block cavity. The WBS has unique self spring properties fixed into the cavity by simply pressing the seal into place. The benefits are:

  • Fire Proof Sponge (WBS) – Ensure optimum durability and moisture protection as well as offering continued thermal insulation within the cavity section.
  • Powerful Intumescent Seal (VWBS) – In the event of a fire, the intumescent seal expands, filling the ventilation and moisture holes. Therefore, stopping the spread of fire and smoke.

Furthermore, the rubberised intumescent stops moisture impregnation.

Cavity Barriers are pieces of fire-stopping material. They fit within the cavity of a building at each floor horizontally and party wall in a verticle position. The material provides compartmentation. Both the flames and heat cannot be transferred to other compartmental areas. Throughout the life of the building, the Cavity Barrier will remain fixed in place. In the event of a fire, the intumescent material expands and seals off the gaps. Additionally, the horizontal barriers allow for a ventilation gap within the cavity. Subsequently closing when the intumescent expands.

Our Cavity Barrier range at Envirograf® offers superb protection to your building by providing fire stopping. Explore the Cavity Barrier range online.


– All barriers in the range are designed to fix across the gap between the inner and outer course of brick to block or block to block walls
– The WB foiled cavity barrier range is designed to be fitted horizontally between brick or block walls, expanding to form a complete fire and smoke barrier in a fire
– Foiled cavity barriers are designed to allow insulation material to be installed both above and below the barrier
– VWBG barrier is self-draining – ideal for allowing free air flow in and out of cavities where smoke sealing is required
– The WBS flexible sponge barriers can be fitted horizontally or vertically between brick or block walls, resisting fire and smoke. The ventilated version, which must be fitted horizontally, is also fitted with an intumescent strip which expands to fill ventilation holes in a fire
– Sponge cavity barriers provide their own thermal insulation, but also allow for insulation material to be installed above and below the barrier
– Tested to BS EN 1363-1 1999, achieving up to 132 minutes fire protection.


Application Instructions

The barrier is held into the horizontal position by sandwiching it between the bricks and mortar at the
build stage. For vertical fix using clout nails.

The barrier is tucked into the brick mortar during build stage, It is then held and fixed to the wooden partition by being pushed into position , because the barrier is flexible it has spring tension and will hold its self in position.


The cavity barrier can be attached to the concrete/steel by means of a metal fixing strap FB/c1 1250mm long or FB/c2 2500mm long available from ENVIROGRAF with appropriate fixings The cavity barrier can be formed to the desired profile / shape so that when the cladding is fitted there is sufficient pressure to arch the barrier and form a fire break.


General Fixing Notes
Fix the metal straps with suitable steel fixings or hilti gun.
If the cavity barrier needs to be cut foil tape should be applied to the cut area.
Foil tape can be purchased separately quoting product code ST50

Order References / Sizes

WBS Cavity Barriers

Ventilated fireproof sponge for cavities
Cavity width allow when ordering 10mm wider for compression in cavity.
You can have one or 2 ventilation holes : A 1 hole B 2 holes

Cavity Width        Actual Width     Sponge Thickness
of sponge
VWBS80          80mm         90mm           40mm       Hole type A
VWBS135      135mm      145mm           40mm       Hole type A or B
VWBS165      165mm      175mm           40mm       Hole type A or B
VWBS210      210mm       220mm          40mm       Hole type A or B
VWBS265      265mm       275mm          40mm       Hole type A or B

Cavity Width       Actual Width      Sponge Thickness
of sponge
WBS80           80mm          90mm          40mm
WBS135      135mm        145mm          40mm
WBS165      165mm        175mm          40mm
WBS210       210mm       220mm          40mm
WBS265       265mm       275mm          40mm