Intumescent Seals is a division of Dixon International Group Limited


THERM-A-STOP range for use in fire resisting door assemblies image

The installation of intumescent fire and ambient temperature smoke seals around fire door assemblies is essential to meet the requirements of the Building Regulations. For some applications fire only seals are acceptable but for life safety smoke control is essential. Once activated intumescent seals will contain hot smoke but cold smoke protection requires the addition of a cold smoke seal which is normally incorporated into the intumescent seal.


THERM-A-STOP has been designed for use in fire resisting door assemblies which have been designated as smoke control doors. The seal slows the spread of smoke and fire through a building by reducing the flow of smoke and air through the gaps between the leaf and the frame or an adjacent leaf edge during the early stages of a fire. The reduced flow of air through the door assembly also restricts the growth of the fire by reducing the amount of oxygen available.

Activated by heat, the foam rapidly expands sealing the air gaps between the leaf and frame, forming a compact mass of heat resistant graphite insulating and retarding the spread of the fire through the doorset.

THERM-A-STOP is suitable for use on fire resisting door assemblies manufactured from timber, or timber doors with steel frames.


THERM-A-FLEX graph image

THERM-A-STOP intumescent fire and ambient temperature smoke seals are available in PVC holders which are 4 mm nominal (actual 4.3 mm). For most latched single-leaf, single swing 30 minute (FD30S) timber fire resisting door assemblies, a single 10 mm x 4 mm or 15 mm x 4 mm strip down each jamb and across the head will usually be satisfactory.

Most latched single-leaf, single swing 60 minute (FD60S) timber fire resisting door assemblies will satisfy the requirements of BS476 : parts 20 and 22 (1987) test procedures when fitted with a single 20 mm x 4 mm strip across the head and down both jambs. Tests carried out to BS EN 1634-1 often require more specific solutions e.g. twin 15 mm x 4 mm seals to achieve a 60 minute rating.

The intumescent foam produced by THERM-A-STOP is designed to withstand high temperatures - so it is well suited to applications incorporating timber doors with steel frames where conventional intumescent foam compounds break down.



The THERM-A-STOP formulation is based on expandable graphite. The seal is supplied in a PVC casing. Unlike many other types of intumescent material, THERM-A-STOP is unaffected by atmospheric moisture and therefore does not require any further protection. It is also immune to degradation by carbon dioxide in the atmosphere.

THERM-A-STOP contains a high density ambient temperature pile seal which has a polypropylene fin for improved smoke and air control at lower temperatures. THERM-A-STOP intumescent fire and smoke seals are also designed to perform the function of a conventional draught seal in daily use.


THERM-A-STOP colour swatches image

THERM-A-STOP is supplied as standard in brown, white, black, grey, cream, red and a light oak woodgrain finish but other colours are available to order.*

Nominal sizes are available in the following dimensions:

  • 10 mm x 4 mm
  • 15 mm x 4 mm
  • 20 mm x 4 mm
  • 25 mm x 4 mm
  • 30 mm x 4 mm
  • 38 mm x 4 mm

The height of the pile projects 5 mm from the PVC holder - and is generally suitable for sealing an average gap of 3 mm to 4 mm between door and frame. The standard pile is grey with a fin but black is available and both colours may be supplied with or without a fin. Other colours are available on request.

If wider gaps have to be sealed, it may be necessary to consider a wider profile.

* Colours may vary slightly between examples illustrated in print, online and actual examples - which will depend upon lighting conditions in situ.

Test Evidence

THERM-A-STOP meets the requirements for fire and smoke performance of BS476 : parts 20, 22 & 31.1 . It has also passed the more exacting standards required by Certifire. It is currently being evaluated to the requirements of BS EN 1634-1.

Copies of test certificates and other evidence are available on request.

THERM-A-STOP - Certifire and IFSA logos

Related Products

Unlatched doors may require additional intumescent material across the head. Latches, hinges, glazed elements, door closers, kick plates, ventilation grilles and other ironmongery may require additional protection in the event of a fire.

Please contact our Technical Department for further advice.