I was looking at these... Sullivan Composite Flex Rod 4-40 48" (1) at Tower Hobbies. They do not change with temp. and are carbon filled nylon. The carbon content is however low enough that the do no cause rf noise.
I use these on the elevators of my Prestige. They do change length with temperature, just not nearly as much as a standard golden rod. The way I have it set up, there's no issues at all with flex, but due to the temperature effects on dimension, I'm not taking this approach in the future.
It's not a huge problem, it's an annoyance. It winds up that prior to the first flight of a day, it's sometimes necessary to bump the elevator trim to get the elevator back to neutral. Unless there is some wild swing in temperature during the day, that's all it takes, with maybe a bump of elevator trim on the first pass , 1st flight. Part of this is also the fuselage changing dimension (especially with humidity changes), so it's not all to blame on the CF rod.