1. There is a custom for men to wear a kittel (white robe) at the Seder. There are two primary reasons for this custom: A) The kittel resembles the ministering angels, who are clothed in pure white. According to this reason, the kittel symbolizes angel-like freedom from sin and it would generate feelings of happiness. (See Hilchos Pesach Rav Shimon Eider and Netai Gavriel Pesach 2 chapter 64) B) The kittel resembles shrouds. Since at the Seder we conduct ourselves like free men and royalty, we are afraid that a person may tend to become haughty. Therefore, the kittel reminds him of the day of his death. (Taz 472:3)
2. The custom of Sefardim and Chabad Chassidim is not to wear a kittel at the Seder. (See Haggadah Shel Pesach Chabad and Netai Gavriel ibid.)
3. The custom is not to enter the bathroom while wearing a kittel, since it is considered a garment set aside for prayer (on Yom Kippur), entering the bathroom with the kittel is not an honorable act. Therefore, if one needs the bathroom during the Seder he should remove the kittel before entering the bathroom. (Beer Heitiv 21:3)
4. Many, including Square Chassidim, do not wear a kittel during the first year of marriage, or shana rishonah. (See Maharam Shick O.C. 28, Katzeh Hamateh on Mateh Efraim 619:11 and Netai Gavriel Pesach page 318) This is also the view of Harav Chaim Kanievsky shlit”a. (Sefer Yismach Lev Nisuin)
5. Others maintain that it is preferred to wear the kittel during the shana rishonah. Vizhnitz, Nadvorna, Sanzer, and Munkatch Chassidim wear the kittel during the shana rishonah. (See Netai Gavriel ibid.) This is also the view of Harav Shlomo Zalman Auerbach zt”l and Harav Chaim Pinchas Sheinberg zt”l. (Haggadah Shel Pesach Harav Shlomo Zalman and Yismach Lev)
6. Above we cited two reasons to wear the Kittel (1. To symbolize angel-like freedom from sin. 2. To remind us of death so that one will not become haughty) There is a great debate amongst the authorities whether a mourner wears a kittel. The Taz (472:3) favors the second rationale for wearing a kittel (so that one will not become haughty) and therefore he writes that a mourner should wear a kittel. This is also the view of the Baal Hatania (472:4), Harav Yaakov Emden zt”l (Siddur), Harav Yekutiel Halbestam zt”l (Divrei Yetziv 208) and Harav Shlomo Zalman Auerbach zt”l (Haggadah).
7. However, the Magen Avraham maintains that according to both explanations of a kittel’s significance, a mourner at the Seder should not wear one. Certainly, if wearing the kittel symbolizes angel-like freedom from sin, it would generate simcha and is inappropriate for a mourner. But even if the kittel is meant to induce humilty, it is unnecessary for a mourner to wear it since he is already saddened. This is also the view of the Bach. Harav David Feinstein shlit”a (Haggadah Kol Dodi) writes, “Magen Avraham’s reasoning is sound, and his ruling is therefore definitive; especially since the Gra, according to the Haggada of Rabbi Yechiel Heller, holds that the rationale for wearing a kittel is that we resemble the ministering angels.” The Mishnah Berurah writes that the custom is not to wear the kittel, however, those that choose to wear one should not be rebuked. For normative Halacha, a rav should be consulted.