On my transitions, no leakage WHATSOEVER! I'll take that to the bank. If that means its space shuttle caliber then so be it. When you seal from the inside and silicone the front piece there will be no air leakage. As for the rec duct thats a different story, not sealed 100% but pretty darn good. No matter which way you slice it sheet metal is superior to ductboard... The insulation in the airstream doesn't bother you? Thats why I dont use soundliner on the supply side of sheet metal duct.
Originally Posted by genduct
America; first we fight for our freedom,
then we make laws to take it away.
-Alfred E Newman