The only tallit I know of that has an all wool atara is the Beit Yosef Tallit, which is marketed for Sephardim. Is there a specific source for this or is it simply being machmir to wear an all-wool tallit?
The Aruch HaShulchan - Siman 8 Seif 10 - who to my knowledge was not a Sefardi - writes:
וכן נכון לעשות שלא יהיה בהטלית רק צמר
And so it is correct to do: to make the tallit only out of wool.
It is interesting that Ashkenazim do not seem to be particular about this, yet Sefardim are!