A proper Sukka is defined by Halacha as a structure consisting of three walls that is covered by Sechach. Hacham Ovadia Yosef, in his Hazon Ovadia Sukkot (p. 1; listen to audio for precise citation), writes that any material may be used for the walls of the Sukka. Unlike the material used for the Sechach, which must meet certain requirements, the walls may be made from any material. Thus, for example, a person can use barrels or the side of a large chest as one of the walls of the Sukka, even though such objects are susceptible to Tum'a, ritual purity (as opposed to Sechach, which must not be susceptible to Tum'a).
Hacham Ovadia adds that the only restriction that applies to the walls of the Sukka is that they do not sway back and forth when exposed to an ordinary gust of wind. Even if there is no wind in the particular location where the Sukka stands, if the walls are made from sheets and the like and would sway in an ordinary wind, the Sukka is not valid for use. The walls need not be strong enough to withstand hurricane-force winds, but they must be able to remain in place when subjected to common gusts of wind.
Hacham Ovadia rules that such walls should not be used for the Sukka even if they are tightly tied to the Sukka's frame such that they do not sway in the wind. Sheets tied to a frame have the tendency to become loose, and the person might not realize when this occurs. He will then be eating in an invalid Sukka which is, in essence, the same as eating outside a Sukka and reciting a Beracha Le'vatala ("wasted" Beracha). Hacham Ovadia therefore maintains that one should use walls that are strong and sturdy, such as walls made from wood, fiberglass and the like, rather than use materials such as canvas that sway in the wind. This is the view of several other authorities, as well, including Rabbi Shlomo Zalman Auerbach (Jerusalem, 1910-1995).
Summary: Any material may be used for the walls of the Sukka, provided that it does not sway back and forth when subjected to an ordinary wind. Even if one ties the material tightly to the Sukka's frame such that it remains in place in the wind, one should not use such a Sukka. Instead, one should use a Sukka made with strong, sturdy walls, such as from wood or fiberglass, that can withstand an ordinary gust of wind.
