Intumescent Seals is a division of Dixon International Group Limited


THERM-A-FLEX has been available for more than 20 years and was the first UK manufactured exfoliating graphite based intumescent product. It has established itself as a market leader giving the benefits of flexibility and resistance to atmospheric degradation. No special protective measures are necessary to ensure that this product will expand on heating when required to do so.

The material will conform to accommodate tight corners, pipes or tubes, and this is one of the factors which ensures its superiority in performance and application when compared with other intumescent strip seals.


THERM-A-FLEX is a general purpose intumescent material offering the qualities of a high expansion foam with a firm pressure to provide the qualities required of an ideal intumescent material for most applications.

The product is designed to withstand a full range of environmental conditions, allowing it to be used in either open or concealed situations without special protection. The flexible nature of the material also permits it to be used for many applications where a rigid strip would be impractical.


THERM-A-FLEX exfoliating graphite based intumescent product graph

THERM-A-FLEX has been developed for general sealing applications but it is particularly suited for the following type of installation:

  • sealing gaps between elements of construction;
  • sealing gaps between fire resisting doors and frames, shutters, windows and the adjacent walls;
  • sealing services into walls or even for sealing voids within services.

Recommendations on the amount of THERM-A-FLEX necessary for the above applications cannot be made, because this will vary according to the size of the gap or void, the nature of the bounding materials, and the period of fire resistance required.

Intumescent Seals will be pleased to offer advice on the quantity of materials likely to be needed for any specific application.


THERM-A-FLEX is formulated from a unique chemical formulation based upon expandable graphite in a binder that allows the material to flex at normal room temperatures. This flexiblility reduces as the temperature nears freezing point. It is not recommended that the material is used at temperatures below 5°C.

THERM-A-FLEX exfoliating graphite based intumescent product graph

THERM-A-FLEX is supplied in its natural black* finish which because of its resistance to both atmospheric moisture and carbon dioxide, requires no additional protection. The material may be decorated with a wide range of conventional finishes without impairing its performance.


THERM-A-FLEX colour swatch

THERM-A-FLEX is available in the following sizes:

  • WIDTHS - up to a maximum of 130 mm.
  • LENGTHS - 1050 mm and 2100 mm as standard (other lengths are available on request).
  • THICKNESS - 2 mm as standard but the range is currently from 1mm to 10mm.

Test Evidence

THERM-A-FLEX 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-FLEX - Certifire and IFSA logos