Acetate is a textile that is made with deconstructed wood pulp,which is known as cellulose. After the cellulose is reacted with acids and other chemicals, acetate is produced. Acetate feels more "natural," more organic, and less artificial than other synthetic hair types. Truly, the best comparison that we can give you is that it feels like the hair of a persian cat. We are not aware of any dolls/toys that are, or were, factory-rooted with acetate. You can't buy acetate doll hair anywhere but Dollyhair!
Acetate's tensile strength is probably the weakest of all synthetic doll hair types, so you don't want to apply too much tension to it when you're rerooting your doll, or you can get a little breakage. It's nothing to worry about, though, especially if you're not a first-time rerooter..
Here is a photo of a doll who was rerooted with acetate hair: