Double wall stove pipe has a 3/8? air space between inner and outer pipes that provides superior insulating value to single wall pipe. Better insulating value keeps flue gas temperatures higher. This helps your wood stove perform with an enhanced draft and provides: Less chance for moisture or soot build up within the vent Reduces smoking of the stove at start up Increased heat efficiency ICC 6UB1F Please read description carefully, item is non-returnable.