Cover Tefillin on Arm

Question: Is it important to cover the tefillin shel yad with one's sleeve?

Answer: The Gemara (Menachos 3b) teaches us, based on the Passuk (Shemos 13:9) “vehoyu lecha leois (it shall be a sign for you),” that the tefillin shel yad should be placed on the upper arm, which is typically covered, as opposed to the hand which is usually exposed.

The Rema (OC 27:11) writes that one does not need to be overly particular about covering the tefillin shel yad. However, the Shulchan Aruch Harav (OC 27:8) states that if one has a bandage on their arm and must wear their tefillin over it, they should cover their tefillin.

The Elya Rabba (27:17) cites the Levush who asserts that the tefillin shel yad should be covered regardless. He questions why the Rema does not require this, especially since the Gemara implies its necessity. Thus, the Mishna Berura (27:47) notes a preference for covering. The Shaarei Teshuva (27:17) cites the Chida (Birkei Yosef OC 27:5), who writes that there are kabbalistic reasons for doing so, adding that one should pull down one’s sleeve after donning the tefillin shel yad. Similarly, the Ben Ish Chai (Vayera 1:15) writes that even when davening alone in a dark room, one should cover one's arm (see Kaf Hachaim OC 25:33).

The Aruch Hashulchan (OC 32:88) frowns upon the use of plastic protective covers on the tefillin shel yad. Nevertheless, the Zichron Yehuda (1:16) quotes the Maharam Schick, who asserts it’s laudable to affix such a box as it prevents the tefillin from becoming passul. Similarly, R’ Avraham Yitzchak Kook (Orach Mishpat OC 9), R’ Ovadia Yosef (Yabia Omer OC 8:4) and R’ Shmuel Wosner (Shevet Halevi 8:8) approve of the protective covers, though they advise removing them while donning the tefillin and affixing them only afterward (see Piskei Teshuvos 27:n199).

In conclusion, it is commendable to cover one’s arm by pulling down one’s sleeve. It is advisable to keep the protective cover on one’s tefillin shel yad, ideally affixing it after donning the tefillin.