Antron and Zelon (both Betts and Blue Ribbon's) are similiar but not identical. Zelon is a finer material than Antron. This might matter to you most if you are using Zelon for shucks on emergers, or maybe posts on parachutes. If you are just twisting the Zelon for a segmented abdomen such as on a Serendipity, then Antron would work just as well. Conversely, I prefer to use Antron yarn (from cards or the spooled stuff) when building bodies and anytime when I'm less concerned with the using a heavy material. In a pinch, however, you could use either interchangeably.