Double-walled stainless steel pipe. I wouldn't take for granted that this will be your situation but it is definitely what we have experienced. I am not an expert like the bean dicks on this site but those are my experiences with double-walled stainless steel insulated chimney.
Sent from my LG-D851 using Tapatalk
Mine is not the insulated type, just double walled. the double walled with insulation was $400.00 per 30" section it was too rich for my bank account. mine is just double walled and cost 150.00 per 30" section. it is claimed to be immensely better compared to single walled pipe, but not as good at the double walled with the insulation.
I used the double wall due to not having a lot of clearance in the space that houses the chimney pipe. There is actually an internal space that goes up inside the wall between the bathroom and the living room that originally had a 4" oil burner chimney in it that the PO had removed and blocked off at the roof.
it measured basically out at 2.5' x 2' so I just climbed inside it, and lined it with the the fireboard all the way to the roof to make it safer from radiated heat from the chimney flue. originally I was going to cheap out and use single wall but before buying my chimney I read a bunch of articles on line about chimney fires, creosote and other safety issues and everything I read said that if you use a double walled pipe it does not radiate out nearly as much heat into the surrounding structure and it helps to alleviate creosote because the hot gasses move faster through it and do not cool down as much prior to exiting. being that my pipe is indoors except for the last couple of feet that should help too.