If someone wears a toupee, must he take it off when putting on Tefilin Shel Rosh? The Tshuvas HaRashba (1:30), which is not in accordance with the other Rishonim, proves from the Yerushalmi that having a Chatzitza, a separation between your head and your Tefilin Shel Rosh, is not a problem. It is only a problem by Tefilin Shel Yad. However, says Rav Menashe Klein (Mishneh Halachos 6:8), says that at best the Rashba only holds this B’Di’eved and even so he concedes that the Rishonim before him disagreed. Furthermore the Rashba says that his opinion is L’Halacha but not L’Maaseh.Another possible heter says the Mishneh Halachos is a Pnei Aryeh (6) who says that if you put white powder in your hair, it is not a Chatzitza since it is for beauty, and anything put in the hair for aesthetic purposes in not a chatzitza. Similarly, says Rav Menashe Klein, maybe a toupee, which is meant to enhance your appearance, is also not a chatzitza. However he dismisses this argument saying that you cannot compare powder, which disappears and a toupee, which is very thick.
L’Maskana he says that the Shela HaKadosh holds that even if you put ashes in your hair for aveilus Zecher L’Churban, you must wash it off before putting on your tefilin. The Machatzis HaShekel (OC 27:4) says that even excessively long hair is a Chatzitza. Although some disagree with this Machazis HaShekel, says Rav Menashe Klein, certainly when it comes to a toupee, all would agree that it is a chatzitza. If after explaining to someone the problem with a toupee for Tefilin the person insists on putting Tefilin on top of a toupee, he definitely shouldn’t make a separate bracha on his tefilin shel rosh.