What is most important is to not to over shrink. If you take the fabric past its limit there is a good chance the fabric will slacken just being out in the cold. Not thermal shock. It looses all it elasticity from too much heat. Under shrinking is always safest. I like 325 to be safe. Some airframes cannot take more than 325. Calibrating the iron often is just as important. Using 325 your iron will bounce up to the 340 mark or so. Even the best irons bounce in temps. This my third fabric job, it is not a shrinking problem.
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