About 10 years ago, I had three 10" diameter runs of insulated flexible duct
installed by an HVAC contractor to go from my basement forced air furnace
plenum to a 2nd floor attic room, hoping to provide adequate cooling and
heating to the 2nd floor attic area. Each of the 3 runs is about 25 feet
long.

I have never been able to get really adequate cooling or air flow on the 2nd
floor, and can only assume that the static pressure drop on these flexible
ducts must be much higher than rigid ducts of the same approximate diameter
and length. The installer was very careful to avoid any sharp bends or turns
in the ducts when installing them, but they really seem to have a lot of
pressure drop.

Is there any easy way to predict how much of an improvement I might expect
by tearing out these flexible ducts and replacing them with the same size
rigid 10 inch circular ducting?

The HVAC contractor who designed and installed this arrangement apparently
over-stated / over-estimated the flow / volume capacity, and the CFM
delivery rates were highly optimistic. I get very little cooling, and better
but not great heating.

Thanks for any opinions in advance.

Smarty