There are many reasons to opt for Rigid Metal Ducts but here’s a few highlights.
-smoother interiors mean better air flow
-rigid metal is more likely to be installed without constrictions whereas flex duct can easily be pinched down
-rigid metal is installed then mastic is applied to air seal THEN insulation is applied on the outside so there is less chance of fibers getting into your air stream
-rigid metal is straight and smooth walled, you have to work to crush or kink rigid metal
-rigid metal is not easily damaged by rodents and UV light