I got the Berk Tuning Mid pipe, which was $45!! It is stainless steel, but unfortunately...it produces more hot air!

 

how does the midpipe produce more hot air?

 

the metal conducts the heat generated by the engine which heats up the pipe which, in turn, heats up the air within mid-pipe.

the moving air within the pipe does cool the metal a bit from convection, but the heat has to end up somewhere