Cotton vs. Rayon vs. Acrylic is all the difference is. I have bought chenille that would normally be used for knitting and used it for fly tying. It doesn't keep the bright color that Rayon fly tying specific chenille does a lot of times but it catches fish. The hardest part is finding the bright colors we use so much. That and some of the stuff you find is flat instead of rounded like the first picture. If you really want bushy full bodied jig get the Lion Brand yarn. Hundreds of fibers that stick out and make a really bushy buggy looking pattern.

Bright color Rayon Chenille

As long as it is color fast and good quality I think any chenille will work