I really like using ep fibers, which are essentially hanks of bulk polypropylene yarn. I buy Congo hair from fly tyers dungeon because it's the same thing as ep fibers but a third of the price. Comes in lots of colors including bright ones, and there is a coarse and a fine variety - the fine stuff at fly tyers dungeon is called "water silk" or something like that, and is good for smaller parachutes and spinners.
Great thing about Congo hair is that the fibers are really long, and you get a ton in a package, so you can leave the post pretty long while you're tying, then trim it to your liking once the fly is finished.