You should never use a heat gun to shrink polyester fabric. Always use a calibrated iron. The 21st Century iron has temp marks on it but should still be checked the first time. Polyester fabric shrinks 5 per cent at 250 degrees F and 10 to 12 per cent at 350 degrees F. At about 400 degrees it begins to lose its memory. At 426 it melts. With a heat gun, you never know what temp you actually hit. Yes it shrinks but how much?

Check out http://www.stits.com/RC_Model_instru...html#shrinking for a summary on heat shrinking fabric.

The dope sold now days shrinks very little unless you specify "Tautening" dope. We rarely use tautening dope because it doesn't chemically bond and as it tightens it may pull away from the polyester fabric. I know following posts will deny that has happened in 75 years of modeling. Mostly because we used to use silk and dope or silkspan which we depended on the dope to shrink and tauten for us. When full scale switched to polyester fabric we found out it doesn't chemically bond hence the need for Nitrate dope first. Then, Ray Stits came along and gave us a system that all chemically bonds from start to finish and dope faded into a barely used method. Only the "I have used dope for 50 years and never had a problem" guys are the only ones that use dope. We are now into the 21st Century and have some vastly improved techniques.