Q. Can the cover of the challos on Shabbos be transparent such as a plastic bag?
A. The Tur (O.H. 271) quotes Talmud Yerushalmi that the challah is covered so that it should not feel embarrassed for not being chosen for kiddush, since according to the verse describing the bounty of the Land of Israel – “A land of wheat, barley, grape, fig and pomegranate; a land of oil-olives and date-honey” (Devarim 8: 8) – it is the bread that should take precedence in the order of brochos.
Therefore, some Poskim are stringent and maintain that a transparent, see through, or with open spaces cover should not be used. (B'riss Olom - Kiddush 35, Minchas Shabbos - Shiyore Hamincho 77, Nishmas Shabbos p. 75, et. al.).
Shemiras Shabbos K. quoting Horav S. Z. Auerbach zt'l permits their use. Others assert that the cover should be white as a signal to the color of the monn. (Tehila Ledovid 271: 13).
Horav Shlomo Miller's Shlit'a opinion is that on the onset (lechatchila) a proper cover should be used. However, at the time one partially uncovers the chalos, places his hands on them and recites the brocho, a remaining plastic cover will suffice.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a.