Dumb questions about rigid flue liner in 8" terra cotta

[302w]

I am sorry if this was posted before. I did search quite a bit!

I'd like to install a 6" liner in my 8" terra cotta chimney. I believe this requires 1/2" insulation to meet code.

Is there any reason that I can't use 6" rigid stainless chimney liner wrapped with 1/2" insulation? I read one post where users responded saying it won't work. Terra cotta is 8" ID, and the wrapped liner is 7" OD with insulation. I'd like to use insulated Duraliner, but it is $100-$150 more for a 4' section.

Is there any advantage to using a flex liner over a rigid liner for a straight chimney? It seems like flex liners are significantly more popular and a bit cheaper.

Thank you!

 

[retlaw]

I have an interior brick chimney with 3-8 x 11 tiled flues. I was able to use Heat Fab/Selkirk 6" rigid liner from cap to cleanout. I used the 24" aluminum faced 1/2" insulation wrap successfully. It was a tight fit. Any protrusions will snag on the leading edge of the insulation.
I have no experience with flex liner but this rigid stuff MUST be way more durable. I would guess most people use it because its easier to install. Dropping/shoving any insulated liner down an 8" tile will be dicey. I would expect some of the flimsier insulation to snag and tear. Did you measure your 8" tile? Mine was less than 8".