In recent times, people have begun to make sukkot with metal frames and walls made out of various types of thick cloth and fabric, like canvas, polyester, and plastics (often with brand names like Pe’er Lanetzach and Ease-Lock Supreme). These sukkot are popular because they are cheap to make, easy to market, simple to put up and take down, and convenient to store. However, some contemporary poskim question their validity because sukka walls must be stable. If they can be blown back and forth by the wind, they are invalid.
Nevertheless, in practice, these sukkot are kosher. The Rishonim objected to fabric walls that were not fastened at the bottom, so when wind blows, the walls rose more than 3 tefaḥim from the ground, invalidating them as walls. There was also the possibility that the wind would blow them away entirely. However, neither of these concerns applies to contemporary sukkot, since the fabric is fastened well all the way around. Therefore, these sukkot are kosher and the berakha may be recited in them. Those who are fastidious may add poles to create lavud walls.
Those who wish to show concern for the stringent view should place horizontal bars no more than 3 tefaḥim (22.8 cm) from one another, up to a height of 10 tefaḥim (c. 80 cm). The gaps of under 3 tefaḥim are considered lavud, and so the bars constitute a wall even without the fabric. However, many make a mistake when they implement this stringency, relying on R. Ḥayim Naeh’s view that 3 tefaḥim is 24 cm, whereas it is actually only 22.8 cm. If the distance between the bars is greater than that, lavud no longer applies to them (as we explained in note 1). Nevertheless, the sukka is unquestionably kosher, as the halakha here follows the lenient view.