I just used a polyester filling to stuff it with.
Also note if you download the German version... I suggested some changes to her which included using a tight decrease/increase on the head. She didn't say which one so I used the yo ktbl which is too loose when you're going to be stuffing. She also used a set of 5 dpn for the frog, but I prefer 4 which made the increase/decreases not even on each needle. This messed me up so I used magic loop with no problems.
When she posts the English version I'll let you know in this thread.