Rav Shlomo Zalman Auerbach once attended a kiddush where no kiddush cup or even glass cup was available. Rav Shlomo Zalman did not hesitate to make kiddush using a plastic cup. When someone mentioned that Rav Moshe Feinstein said it was assur to use a throw away cup. Rav Shlomo Zalman did not flinch and said it is mutar beyond a shadow of a doubt. Rav Shlomo Zalman gave a Mashal to shirts that are made for one time use and sold in America. “If I had a shirt like that” said Rav Shlomo Zalman, “Do you think I would throw it away after one use?”Rav Shlomo Zalman’s son-in-law, Rav Zalman Nechemia Goldberg proved from the Rambam that any vessel meant for one time use, is not considered a Keili. However he says that it depends on the users intention. If does not plan on throwing it out, then it is a Keili, even if he is the only one in the whole world that reuses it.