904L Midflex Midtherm Flue Liner Published July 18, 2018 at 1772 × 2362 in Midtherm Midflex Flexible Flue Liner 904L Midflex Midtherm Flue Liner The 904L Midflex Midtherm Flue Liner is laser welded and double lined. This provides very good strength and durability. Like this:Like Loading...