Yerushalmi Sukkah 1:6 ירושלמי סוכה א׳:ו׳

MISHNAH: One does not thatch with bundles of straw, and bundles of wood, and bundles of shoots¹⁵³The soft shoots of vines which are edible, in contrast to wood which is hard and inedible.; but all of them are qualified if untied. All of them are qualified as walls.

HALAKHAH: Rebbi Ḥiyya in the name of Rebbi Joḥanan: Because it looks like storage¹⁵⁴Tied straw and wood is as impervious to impurity as is untied. The reason one may not use bundles is that this is the way the materials are stored; the prohibition is rabbinic because it makes the roof look like a depository and not like a roof or, as the Babli 12a explains, one might use the space as depository and later change one’s mind and make it the roof of a sukkah; then the roof was not made for the holiday and as such is disqualified..

Rebbi Jacob bar Abbaya, Rav Sheshet in the name of the Great Rebbi Ḥiyya: There is no bundle with less than twenty-five¹⁵⁵Therefore small bundles may be used as roofing when still tied.. Ḥinena bar Shelemia in the name of Rav: If he cut for roofing it has no handles¹⁵⁶In general, only edible produce can become impure. But inedible stems to which produce is attached transmit impurity to the produce; the detailed rules are given in Tractate Uqeṣin. It is stated here that if grain is cut as roofing, the straw only has to be more than the grain kernels. No inedible part of the stalk has to be compensated for. Babli 13b.. If he cut as roofing and then intended it as food it follows his thought¹⁵⁷And become disqualified as roofing by his thought.. If he cut for food and then intended it as roofing? Others say, only if the straw is more than the food and the handles¹⁵⁸The shells and the ends of the stalk also have to be compensated for by straw. Babli 13b.. Rav follows the others. Where do we hold? If he cut for roofing but it became prepared and he said, after they will have fulfilled the commandment I shall bring them back to the threshing floor, do they need preparation a second time or are they already prepared¹⁵⁹In general, produce becomes susceptible to impurity only by contact with fluid desired by or desirable for the owner. This is called “preparation for impurity”, cf. Demay2:3, Note 141.
The question is not answered. Therefore it is possible that the material is susceptible for impurity, disqualified as roofing, and prepared for impurity as food. No answer is support for the second alternative. Babli 13b.?

Rebbi Yasa in the name of Rebbi Ḥama bar Ḥanina: You shall cover the Ark with the cover¹⁶⁰Misquote of Ex. 40:3; scribal error. Instead of “cover” it must be “gobelin”. Since the gobelin was the dividing wall between the Ark and the interior of the Tent, the intended meaning is: You shall hide the Ark behind the gobelin.. From here that the wall is called cover. From here that one makes walls with matter susceptible to impurity¹⁶¹Since the root סכך is used, it follows that all that is acceptable as roofing a sukkah is acceptable as wall. Since the gobelin is mentioned which is susceptible to impurity, walls may be made from matter susceptible to impurity. Babli 7b..