Bundles of straw, bundles of wood, or bundles of fresh cane, may not be used for s’chach; but all of these are valid when they are untied.  All of them are valid for the walls.

We may cover the succah with boards; these are the words of R’ Yehudah. But R’ Meir forbids it.  If one placed atop it a board that is four handbreadths wide, [the succah] is valid, except that one may not sleep under [the board].