Take a garden hose and put it between your two hands in a straight
line. If you just bend the center line it it will give easy. But if you
try keep the center line straight and rotate one hand one way and the
other other way it will resist. A very soft rubber hose might give in
such rotation but not a stiff one. In the same way most of the
"flexible" ducts do not really give in such "shear" rotation and are
"stiff" - especially if they have a wire helix coil inside. My engine
setup is exactly such that the yield needed is in "shear" along the
center line for a short piece of ducting.

Morgans wrote:
I must not fully understand how it is going to be used. How many degrees of
rotation are you thinking it will have to put up with?
--
Jim in NC