Metal flexible liners are used to re-line traditional chimney stacks.  These are twin skin construction; the outer face is usually corrugated, and the inner surface is smooth.  Liners can also be used for gas and multifuel installations. With most house chimneys being quite old now we strongly recommend that a liner is fitted. It improves safety, helps with sweeping (stops the need for access hatches) and improves the overall performance of the stove. We only use top quality pressure tested liners in 316 grade stainless steel (sometimes 904 grade stainless steel where solid fuels are mainly being used). Purchasing cheap liners is false economy. Most liner kits we sell have a terracotta pot hanging cowl for the roof, and an adaptor at the bottom of the liner that then connects to a vitreous enamel flue pipe that in turn connects to the stove.