I used the stuff that Rev pointed out, many, many moons ago. I think it was from JC Whitney. Maybe 20 years ago.
I used it to make side exiting exhaust on an '81 5th Ave. It's like fused spiral steel. If you don't grab hold of enough of it when you clamp it down it'll unwind itself.
It did the job I wanted, being a teenager with little money to spend. (Hey, now I'm an adult with little money to spend
) This was a cheap way to do the exhaust without getting custom bent stuff.
It's not very forgiving as regular exhaust pipe is rigid, this isn't and the weight of itself pulled off this flexible tubing as I was driving in the winter. I had to crawl under in the snow and slush and pull off what ever was left of the exhaust since it was dragging on the road!
Like Barry mentioned, it doesn't last very long. It could work if you used short sections or longer sections with more exhaust hangers. It doesn't bend at very tight angles. It will be prone to leaks at the seems after a while is my guess and MAY not pass a state inspection depending upon where to live.