If a person does not have a regular Kiddush cup, and all he has is a disposable cup – made from paper, plastic, or Styrofoam – may he use such a cup for Kiddush?
Rav Moshe Feinstein (Russia – New York, 1895-1986), in his Iggerot Moshe (3:39), rules that a disposable cup should not be used for Kiddush because it is not respectful to the Kiddush. This is also the view of Hacham Bension Abba Shaul (Israel, 1923-1998), in his Or Le’sion (vol. 2, p. 314). It should be emphasized that according to this view, there is no difference between a single disposable cup and two cups. Since disposable cups are not respectful, even one such cup inside the other does not qualify for Kiddush.
Other Halachic authorities, however, dispute this ruling. Rav Eliezer Waldenberg (Israel, 1915-2006), in his Sitz Eliezer (12:23), maintained that there is no difference between disposable cups and ordinary cups as far as Halacha is concerned. A disposable cup is a perfectly good cup, and it is only because such cups are inexpensive that people discard them after a single use. Practically speaking, they can be used multiple times, and people throw them away after one use only because the cups are so cheap that it is not worth their while to wash them and keep them. Therefore, Rav Waldenberg claims, a disposable cup may be used for Kiddush and for Netilat Yadayim, as from the perspective of Halacha it is no different than any other cup. This was also the position taken by Rav Shlomo Zalman Auerbach (Israel, 1910-1995), and by Hacham Ovadia Yosef, as recorded in Hazon Ovadia – Shabbat (pp. 54-56). Hacham Ovadia ruled that although it is certainly preferable to use a regular metal or crystal cup, strictly speaking, it is perfectly acceptable to use a disposable cup for Kiddush.
It should be noted that this volume of Hazon Ovadia was published only recently, and thus Hacham Ovadia’s lenient ruling on the subject was not known until now. Hence, even if previously we have followed the stringent opinion of Hacham Bension, in light of the new information concerning Hacham Ovadia’s stance on this issue we may certainly be lenient, when necessary, and allow using a disposable cup for Kiddush.
This applies to Netilat Yadayim, as well. It often happens when a person finds himself in an airport or on a trip and wants to eat a sandwich he has access only to a disposable cup. According to Hacham Bension, if all one has is a disposable cup, it may be used, but no Beracha is recited over the washing in this case. He does allow, however, using a disposable cup if one ensures that somebody else uses it after him, so it is used more than once. Once again, however, in light of Hacham Ovadia’s recently publicized ruling, we may follow his lenient position and allow using a disposable cup for Netilat Yadayim, when necessary. This is Rabbi Bitan’s conclusion in the English edition of Yalkut Yosef – Berachot (vol. 1, p. 118; listen to audio recording for precise citation), though he advises that one satisfy Hacham Bension’s opinion by ensuring that the cup is used at least once more after he uses it for Netilat Yadayim.
Summary: It is preferable not to use a disposable cup for Kiddush, but strictly speaking, such a cup may be used. If one has only a disposable cup for Netilat Yadayim, he may use it, though he should preferably see to it that the cup is used at least once more after he uses it for washing.