Insulating your stainless steel chimney liner is highly recommended. Chimney liner insulation helps ensure safety and efficiency of the chimney liner. Insulation allows for the flue to heat up more quickly and at a higher temperature. Since the flue gasses are staying hot, less creosote will form. Your chimney flue will stay cleaner longer because there is less buildup. In addition, less fuel will be used.
There are two common types of chimney insulation: blanket wrap and pour-down mixture. The chimney insulation blanket wrap is the most popular because of how user-friendly it is but it will add 1.5" to the overall diameter of the chimney liner. The vermiculite pour-down mixture is the best option when the flue is tight, or a chimney liner has already been installed. The pour-down mixture will also fill any dangerous cracks in the masonry work.