Insulating ducts in unfinished basement?
There are products specially made for wrapping the metal HVAC ducts.  Its not recommended to use wall insulation (your 40-ft roll) with HVAC because it isn't designed to handle the temp changes.

Before you insulate the ducts they should be properly sealed with mastic or foil tape.  This basically means cleaning the dirt/dust off of the duct before sealing.