The inert nature of clay makes the final product resistant to rust and corrosion caused by the by-products of combustion in the furnace. The smooth surface inside the clay flue liner resists creosote build-up caused by low-burning fires. However, all chimneys still need to be periodically inspected and cleaned. Unlike metal, clay is a slow conductor of heat, further minimizing the danger of heating masonry and wood structures surrounding the lining.