I am attempting to knit a felted hat and would like to use alpaca. Will it work for felting?
I know that alpaca blends will felt…but not sure about 100%. The safest thing to do with any yarn you’ve never felted with before is to knit a swatch and give it a try. 
I’ve read that alpaca felts, but not as firmly as wool, if that’s any help.
any animal fiber will felt, including alpaca, silk, etc., and even some blends with non-animal will felt as long as the wool content is high enough, but like the others said, the degree is what differs. your best bet is to felt a gauge swatch. 
I cut my felted gauge swatch into a fabulous little coaster for my desk, so no waste! 