For these, I used Tulle-Organza. It's like a fine-weave tulle with the shimmer of organza (but doesn't shed glitter!) I used a 10' long ribbon down the middle and box-pleated 4 layers of 11" wide tulle. Which is pretty wide, you probably wouldn't want your regular floorshow boas to be that wide, unless you just wanted them to be "extra". Each layer was applied individually, and I just pleated as I went. The dark purple ends are chiffon (and those edges are serged).
This makes a very cost-effective boa - which is great for theme shows (think Pride, Halloween, etc.) Anyhow, the Organza ones are coming soon(ish)!