As others have said it takes more heat to shrink Monokote than another product like Ultracoat. To do any covering job properly and to be able to get out all of those wrinkles, a heat gun is a must. For the best covered finish (with any product) is to seal the edges with the iron, and then shrink the rest of it until its taught with the heat gun. I see too many people trying to shrink an entire wing or fuselage with just an iron.