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Furanflex layers 301x1024

FuranFlex® liners are composed of three layers:

  • Internal layer: thermoplastic tubular film
  • Composite layer: fibre-glass impregnated with heat resistant resin
  • External layer: thin textile cover of artificial fibre
Furanflex layers RWV 301x1024

The setup of FuranFlex® RWV chimney liner is similar, but some of the applied materials are different:

  • internal layer: thermoplastic tubular film
  • composite layer: fibre-glass impregnated with resin of increased heat resistance
  • external layer: thin textile cover of glass-fibre and Kevlar fibre



The internal thermoplastic polyethylene tubular film is needed at the stage of inflating and hardening. Its thickness is 120-150 μm, its melting point is 120 °C. Its task is to provide the required air-compactness, necessary for inflating the liner tube with air and steam. The tubular film then needs to be drawn out from the hardened FuranFlex® and FuranFlex® RWV tubes and is to be disposed in an appropriate waste container.


The heat, flam and corrosion resistant structural material of the FuranFlex® chimney liner is the mid composite layer. The term composite means a fibre-glass reinforced hard thermoplastic resin.


The resin developed for the FuranFlex® chimney liner is a liquid material consisting of the mixture of several components. Its characteristics may be modified with various additives. The thermosetting resin becomes slowly hardened at high temperature. The hardening process consists of three stages:

1. Liquid state
The viscosity at this stage is similar to that of honey. It becomes denser at cold, while it dilutes at warm temperature.

2. Soft, yet, not liquid, so-called „B” state
By the effect of a catalyst, the material is transferred from a fluid state to an already non-fluid state. It can be grasped by hand, can be bent and stored for a certain period of time. By the effect of heat, it slightly softens.

3. Hardened state
By the effect of heat or extended storage time, the resin irreversibly hardens. Once it has hardened, it can no longer be softened again. At this stage, it is already a solid structural material with excellent heat and corrosion resistant characteristics.


In the FuranFlex® material, fibre-glass is applied in the form of textile. The weight of the fibre-glass textile produced from thin cross and longitudinal fibre bundles is 330 g/m2.

The longitudinal fibres of the fibre-glass textile take up the vertical weight of the installed FuranFlex® liner. The cross direction fibres provide the rigidity in the cross section of the chimney.


The fibre-glass textile is impregnated with fluid thermosetting resin, which fills the gaps in between the glass-fibres. After hardening, this forms the composite structure.

The fibre-glass textile is impregnated with fluid thermosetting resin
The resin transfers the forces from one fibre to the others and protects the glass-fibres from corrosion at the same time. The hardness of composite structures is defined by the quantity, type and direction of the reinforcing fibres thinner than a hair. Every square metre of the 2 mm wall structure of the FuranFlex® chimney liner has 3.000.000 meters of elemental glass-fibre each with the diameter of 13 microns. The hardness of glass-fibre equals to that of steel, however, its weight is three-times lighter (2.4 g/cm3).

The mid composite layer, depending on the FuranFlex® type contains 3 or 4 fibre-glass textiles impregnated with thermosetting resin, which constitutes an inseparable unit after hardened.


The hardening of the FuranFlex® chimney liner consisting of resin-impregnated fibre-glass textile and internal foil is carried out by steam. The steam pressure forms the layers of tubular film and resin- impregnated glass-fibre textile to be of larger and larger diameter cross-section.

In order to stop the increase at a certain diameter, an external non-flexible textile tube needs to be drawn on the external surface of the FuranFlex® liner.

The black polyester textile is developed for temperatures below 500 °C, while the white textile of glass and Kevlar fibres is developed for temperatures below 1000 °C.