Question: What must the walls of the Sukkah be made of? Is a Sukkah whose walls are made of fabric (such as canvas and the like) valid?
Answer: A Sukkah must consist of three walls and Sechach (roof of the Sukkah made from objects which grow from the ground). The walls of the Sukkah may be made from any material one wishes as long as they are strong and sturdy enough to withstand an ordinary wind (breeze); if the walls are not sturdy enough to withstand such a wind, they are not valid for the Mitzvah of Sukkah.
Therefore, Maran Rabbeinu Ovadia Yosef zt”l rules that one should not use sheets, fabrics, and the like for the walls of the Sukkah, for they flap back and forth in the wind; even a small movement renders them unfit to withstand an ordinary wind. Even if one stretches these sheets until they are taut and then ties them very well to the poles of the Sukkah so that they do not move in the wind, this is still unacceptable, for sometimes, the knots come loose as a result of the wind and the sheets begin to sway and this renders the Sukkah invalid, in which case anyone who sits in it is in essence not sitting in a Sukkah and any “Leeshev Ba’Sukkah” blessings recited upon it are blessings in vain. Although there are those who maintain that as long as the sheets do not sway very much in the wind (approximately three Tefachim or twenty-four centimeters from side to side) these walls are still valid, nevertheless, it appears from the words of the Rishonim that even a slight movement invalidates the Sukkah. This is indeed the consensus among most modern-day Poskim including Hagaon Harav Yosef Chaim Zonnenfeld zt”l and Hagaon Harav Shlomo Zalman Auerbach zt”l. Similarly, Hagaon Harav Moshe Feinstein zt”l writes that one may not be lenient and build his Sukkah out of sheets of fabric or tarp and he adds that the fact that such Sukkot are sold in the United States (place of Harav Feinstein’s residence) must not have been done in accordance with the ruling of a Halachic authority, for such Sukkot may not be used.
Material Which is Capable of Becoming Impure
We have written that one may make the walls out of any material one wishes, including vessels, such as closets, chests, and the like. Although these items are vessels and thus are capable of becoming impure (meaning that if an impure person touches the vessel it will consequently become impure as well) and such things may not be used for the Sechach of the Sukkah, the walls of the Sukkah may nevertheless be made of things which are capable of becoming impure.
This means that the Sechach of the Sukkah must be made only from material incapable of becoming impure but the walls of the Sukkah may be made from vessels of any other item which is capable of becoming impure.
Nonetheless, the part of the wall of the Sukkah where the Sechach rests is considered “the Sechach’s support” and should preferably be made of materials which are not capable of becoming impure due to an edict of our Sages who were concerned that perhaps one will come to use such materials as Sechach. Thus, if the walls of the Sukkah are made of materials that are capable of becoming impure, such as closets, metal poles, and the like, it is preferable to place a wooded beam on top of the walls or poles around all four sides of the Sukkah in such a way that the Sechach will rest on the wooden beams as opposed to the material which is capable of becoming impure.