Just make 4 pieces about 15mm taller & 25mm longer than distance from mobo to cooler. Folded a flap with the 15mm to fit under bottom of cooler and on ends to glue to next side and keep it flat. Cut openings in each piece as needed; front for fan to blow air in, sides and back for each of the heatsinks on my X58A-UD5. Had to trim a little on bottom to get fit to motherboard over small pieces.
Same technique as other ducts you've seen.
Cardboard tubes are handy for some things too. Like from TP, paper towels, etc.
Edited by doyll - 7/15/13 at 9:26am