There is also welded seam flex liner called ventinox. It is a good liner but it is lightwall. Light wall is .005" or .006" heavy wall is .014" there is also a midweight which is constructed the same as the heavy wall it is just .010"Yes, welded means a rigid liner. The places around here include the installation with the unit. I will look into the type of flex liner. What thickness is considered "heavy duty"?