but ill tell you that you should use insulated duct for the run to roof deck.
say its freezing cold in your attic space. you pump hot steamy shower air into the duct... then you get condensation on the inside of the duct which runs down the sides of the duct back into your fan and possibly into your drywall.
say its hot as all hell in your attic. well then you get heat moving through the duct, then down into the draft damper inside your blower... then slowly heating the damper and re radiating heat into your living space.
its a small amount of heat provided every thing is sealed and working as it should... but its SOME heat. its worth insulating the run of duct.
insulated duct also essentially has 2 layers protecting from air leaking back out into your attic space.
avoid hard elbows. use 5 gore min. elbows with a radius of 1.5 radius to diameter of bend.
strap the duct and secure it well at the roof and at the connection to the fan. the duct should not move what so ever when the fan is energized.