Light Wall Flex – also known as M-flex, Dura-flex, Z-flex, Best-flex, Ultra-Pro and many more names – is a thin, flexible snake-like liner. It is most commonly installed by sliding it down the chimney like a snake until it reaches the bottom where it is connected to the appliance. This type of chimney liner is very popular because it is relatively inexpensive (per foot cost) and it is easy to install, which cuts down on labor costs.

However, this type of liner is prone to creosote build-up because of its corrugated interior (which causes more turbulence of flue gases and thus collects more creosote). In addition, there are durability issues. Because the light wall material is so thin, if it is ever plugged (e.g., by creosote or nesting animals) it can be damaged by a chimney sweep trying to clear the blockage. Bending this type of liner around a metal damper can also be hazardous; because of the lightweight material, the metal-on-metal contact can rip through the chimney liner over time.

Light Wall Flex Chimney Liners


I have a wood stove. Can you use a light wall liner in my chimney?

Chimney Savers strongly recommends rigid or heavy wall liners for wood-burning appliances because they last longer, perform better, and collect less creosote, making them safer than their light wall counterparts.

What type of insulation should I have around my chimney liner?

The type of insulation required is based on several factors, such as the type of appliance the chimney liner is venting and the clearance (i.e., distance) that the chimney has to combustible material (e.g., wood framing around the chimney).

There are two types of insulation on the market for stainless-steel chimney liners. The first type is called “poured-in insulation.” Chimney Savers does not offer poured in insulation, because we don’t believe that it should ever be installed in a chimney. If you are curious as to why and would like to learn more, click here to read our blog post.

The second type is called “insulation wrap.” Basically, it is a foil-faced ceramic blanket, which is wrapped around the liner before it is installed. Once this blanket is wrapped around the liner, a mesh sleeve is pulled on, covering the insulation wrap and providing a layer of protection. This mesh sleeve keeps the insulation from ripping as it is lowered down the chimney. A ½-inch thick insulation wrap is the ideal way to insulate a stainless steel liner because it keeps higher heat in the chimney and away from combustibles, as well as reducing any condensation that may occur inside the chimney liner.

Did you know that, according to NFP211 codes and standards, a masonry chimney with a tile liner must have a 2” clearance to combustibles? In other words, there must be 2 inches from the outside bricks on the chimney to combustible materials (e.g., wood and fiberglass insulation) throughout the house. We have found that most chimneys do not comply with this code. By installing an insulated stainless steel chimney liner you reduce the required clearance to 0 (zero) inches – meaning there can be combustible materials actually touching the chimney!