This is a great product as an alternative to vermiculite (in very big chimneys for instance) plus a lot less messy. Manufactured from rot proof, odourless, non-combustible rock wool. It does not sustain vermin and will not encourage growth of fungi, mould or bacteria and is suitable for continuous operating temperatures of up to 500 degrees centigrade. Also available foil tape for all joints. Pipe thickness is 25mm/1" and lengths are 1.metre/39", they come in three sizes for the following liner sizes 125mm/5" - 150mm/6" or 200mm/8" internal diameters. Actual internal diameters of the tubes are shown below. 200mm/8" internal diameters, they can easily be trimmed to fit 175mm/7" chimney liner. To suit liner size Inside diameter of tube 125mm 140mm 150mm 169mm 200mm 219mm Not recommended on class 2 flexible liners (oil or gas liners)