Midtherm Midflex 316L and Midflex 904L products are twin wall flexible flue liners suitable for lining masonary chimneys, that are competitively priced and manufactured to a high standard.


The products are manufactured from high grade austenitic stainless steel profiled strip which is rolled and seamed in a continuous process and which results in a product with a smoother inner surface and robust outer casing.

Midflex 316L

Midtherm Midflex 316L is a twin wall flexible liner made from 316L grade stainless steel, which offers good resistance to pitting and crevice corrosion.

Where a lower temperature/slumbering operation may be encountered the Midflex 904L product should be used.

Midflex 904L

Midtherm Midflex 904L is a twin wall flexible flue liner made from 904L grade stainless steel (a high performance austenitic stainless steel) with high levels of chrome, nickel, molybdenum and copper which provide it with exceptional corrosion resistance.

The Midflex 904L is extremely resistant to pitting and crevice corrosion and has very good resistance to stress corrosion cracking.



The product’s flexibility enables it to be handled and installed with minimum curvature compared to competitors products while still avoiding any deformation of the inner wall.

Versatility, practical assembly procedure and rapid installation together with the technical characteristics of the product (extremely low fume resistance , rapid temperature stabilisation) ensures the flex system meets the requirements of most operations.

When installing the liner, attention must be paid to the arrows marked on the liner, which indicates the fume flow direction. We recommend that all installations should be back filled or insulated with a high density mineral wool such as Rockwool to improve the resistance to corrosion of the liner.

For full installation details please refer to the Midtherm Twin Wall Installation Instructions.

For more information on the products available from Midtherm Flue Systems Ltd. through Plymouth Chimney & Flue Specialists Ltd please see the Midtherm website.

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