Insulators as follows -- actual postage additional:

1977 Maitland, Florida - 8th convention -- great amber with a cool carbon bubble -- $25

1981 Sacramento, California -- 12th convention - bright emerald! -- $20

1982 Cedar Rapids, Iowa -- 13th convention -- white milk glass -- $15

1988 Houston, Texas -- 19th convention -- ink blue -- $20

2016 Muncie, Indiana -- 47th convention -- bright blue -- $25