The sekhakh is the primary component of the sukka; after all, it gives the sukka its name. Sekhakh must meet the following three requirements:
- It must be made from plant matter.
- It must be detached from its source.
- It must not have been processed in a way that renders it susceptible to tum’a.
Let us explain further.
The first requirement is that the sekhakh must be made from something that grew from the ground, that is, plant matter, like trees and shrubs. Metal, dirt, and plastic, though they originate in the ground, are invalid, as they do not grow. Animal skins are not considered to have grown from the ground, even though they are from animals that were nourished by the earth.
The second requirement is that the sekhakh be detached from its source. Therefore, climbing plants and tree branches are invalid.
The third requirement is that the sekhakh not be susceptible to tum’a (ritual impurity). As a rule, anything in its raw, natural state is not susceptible to tum’a, but after it has been processed and manufactured for human use, it is susceptible to tum’a. For instance, tree trunks, branches, and even straight wooden beams used in building cannot become tamei. But if they are made into articles (kelim) like chairs or beds, they can become tamei and are invalid for use as sekhakh. When an object goes from being raw material to being a significant article, it becomes susceptible to tum’a. Then, if it comes into contact with a dead body or something else that conducts tum’a, it becomes tamei. Once plant material has been processed and become susceptible to tum’a, it is invalid as sekhakh, even if it has not actually become tamei.
Fruits and vegetables that are fit for human consumption are susceptible to tum’a and invalid as sekhakh. However, if they are fit only for animal consumption, they are not susceptible to tum’a and may be used as sekhakh (SA 629:9-11).
A straw or reed mat that was made for sitting or sleeping is susceptible to tum’a and is invalid as sekhakh. However, if it is made to be used as sekhakh or as an awning, it is not susceptible to tum’a and may be used as sekhakh. In a locale where mats are generally made only for sitting or sleeping, then even if one is made for sekhakh it may not be used, because of how it would be perceived (SA and Rema 629:6).
Even though broken parts of beds or other furniture are not susceptible to tum’a, the Sages forbid using them as sekhakh, out of concern that people might mistakenly think that these items can be used for sekhakh even when they are susceptible to tum’a (SA ibid. 1-2).
The Sages forbid using flax as sekhakh once the process of making it into thread has begun, since its natural shape has been altered. Therefore, one may not use paper or cardboard made from wood pulp, since they underwent processing that altered their natural shape. Likewise, cotton wool may not be used as sekhakh (Yerushalmi; Rambam; MB 629:13).