I am looking at the in mesechta Shabbos where it speaks of wearing a head covering. I am wondering if it is a din in halacha or its a minhag Yisrael to wear a double head covering( black hat etc..)
Nechemyah D, Brooklyn
The Tur (OC 8) states that one should cover his head with his Talis Gadol during prayer so that his head is not uncovered during prayer. The Beis Yosef says that the Tur is speaking about someone who is already wearing a Kipah, and he is being instructed to have an extra covering on his head to increase his Yiras Shamayim. Quoting both the Gemara in Kiddushin (29b) and the one in Shabbos that you mention, he says that it is the way of Tzenius to put on a second head covering (see Maharsh"a to Shabbos (ibid.) that seems to come to the same conclusion as the Beis Yosef - heard from Rav Moshe Sternbuch).
The Siddur haYa'avetz also says that wearing two head coverings is the way of the Tzenu'im. He says that the Berochah we make in the morning - Oter Yisral b'Sifarah - is referring to the placing of a hat or turban over one's Kipah.
According to the Beis Yosef, then, it is proper to wear two head covering during prayer ("Nachon sh'Yechaseh Rosho b'Talis"), and - presumably - praiseworthy to wear them at other times as well.
It is important to note that the Gemara in Kiddushin is speaking about a Sudar - some kind of turban. Therefore, it might be that wearing two Kipahs one on top of the other might not have the same effect.
The Vilna Gaon (Biur haGR"A, O.C. 8:2) argues with the Beis Yosef and holds that, m'Ikar haDin (strictly speaking), head covering is not required (even one cover) even for Tefilah and Berachos.
Many Chasidim have a strong custom to wear two head coverings, at least for saying a Davar sh'b'Kedushah. Chabad Chasidim are careful about two head coverings at all times. Customs that distinguish Chasidim from non-Chasidim usually have their roots in the Kabbalah. I don't think there are any explicit statements in the Zohar or Kisvei AR"I on the matter. The best I could find was a statement in the writings of the Lubavitcher Rebbe, Rabbi Menachem Mendel Schneerson (Toras Menachem) that the two head coverings parallel the two highest levels of the Nefesh - Chayah and Yechidah - which are known as Makifim.
Hope this helps.
Kol Tuv,
Yonasan Sigler
This is not a Psak Halachah