And you don't have to sew a single stitch! =)
I used some fleece* from my fabric stash but a piece of cotton flannel would also work. The flannel (or any woven fabric) will fray, but I'm guessing it would hold up at least as long as the catnip stays potent!
Cotton fabric would work too, but likely won't hold up as well if you have rough players. Mine love a larger toy that they can wrestle with and kick! I won't say the canines in the house don't play with these too. ;-)
The size isn't too important. You just need a piece big enough to fold into thirds and tie into a knot so a smaller piece will work if that's what you have in scraps.
Add some catnip - again, amount doesn't need to be specific here. I used about 2 teaspoons per knot.
The added bonus is, these are easily refreshed by undoing the knot and replacing the catnip.
If you have more than one kitty, make a few. Mine tend to hog new toys. LOL
* If you don't have fleece scraps already in your fabric stash and want to use a fleece, look for organic cotton fleece (not polyester fleece). Polyester fleece sheds tiny plastic particles (not good for anyone). Better yet, look through your closet and see if there's a piece of clothing you no longer wear that you can repurpose the fabric into kitty toys! So many possibilities!
Find more information here on how unfriendly polyester fleece is to the environment.