Intumescent Seals is a division of Dixon International Group Limited


Many buildings incorporate linear gaps in their structural design which need to be protected in the event of fire to maintain the building’s fire resistance integrity. THERM-A-FOAM is a simple moisture resistant preformed intumescent seal designed to provide this protection in a cost effective way without the need for adhesives, mechanical fixings or protective sleeves.


THERM-A-FOAM is a preformed linear joint seal comprising one or more layers of 10mm or 20mm flame retardant polyurethane foam coated on both sides with THERM-A-FLEX intumescent material. These layers are combined to produce a product suitable for sealing a range of gaps sizes in building structures.

The flexible open cell foam structure allows THERM-A-FOAM to compress by approximately 50% thereby enabling it to take the shape of the building joint it is protecting. At approximately 180°C the installed THERM-A-FLEX begins to expand. During this expansion the flame retardant foam degrades and is replaced by the expanding intumescent graphite thus providing fire protection to the building joint.


The table below provides a guide to the correct THERM-A-FOAM dimensions for a range of building joint widths and fire resistance requirements.

Fire resistance
1 hr 1½ hrs 2 hrs 3 hrs   4 hrs
Gap width Depth of Firefoam fill required
10 25 25 25 35 40
20 25 25 30 40 50
30 25 25 30 40 50
40 30 30 35 45 55
50 35 35 45 60 75
60 35 35 45 65 90
70 40 40 50 75 105
80 40 40 50 85 105
90 45 45 55 85 105
100 50 50 60 85 105
Linear dimensions in mm          

Allow a minimum compression of 15% to cater for ambient temperature movement changes in the building joint.


THERM-A-FOAM will provide fire resistance of up to 240 minutes for masonery building joint widths of up to 100mm.



THERM-A-FOAM is available in the following sizes:
Length: 1m as standard
Depth: 25mm to 105mm i.e. to meet fire resistance requirements
Width: 10mm to 100mm i.e. to suit gap size.

Test Evidence

THERM-A-FOAM meets the performance requirements noted above in accordance with BS476:part 20. It is currently being evaluated to the requirements of BS EN 1366

Copies of test reports and other performance evidence are available on request.

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