Sukkah 4A

ואף על גב דבטלינהו [לכולהו], משום דבטלה דעתו אצל כל אדם.

And even though he nullified them all, intending that for the duration of the Festival the halakhic status of these cushions and blankets is nothing more than that of dirt, it is not deemed a fit nullification because his intention is rendered irrelevant by the opinions of all other people. People do not typically do so, so the action of one who does so is discounted.

תבן ובטלו הוי מיעוט, וכל שכן עפר ובטלו.

If one placed straw on the floor of his sukka in order to diminish its height, and verbally nullified it by saying that he will not use it for another purpose, it is a decrease of halakhic significance, as the halakhic status of adding straw is like that of adding dirt to the sukka floor and diminishing its height. The same is true, all the more so, if he placed dirt on the sukka floor and nullified it.

תבן ואין עתיד לפנותו, ועפר סתם ⁠— מחלוקת רבי יוסי ורבנן. דתנן: בית שמילאהו תבן או צרורות וביטלו ⁠— מבוטל.

A case where one placed straw on the sukka floor and he does not intend to evacuate it from there, although he did not nullify it, and a case where one placed undesignated dirt that was not nullified, are the subject of a dispute between R' Yosei and the Rabbis with regard to whether the actions alone are effective as nullification. As we learned in a Mishnah: In a house in which there is a corpse or an olive-bulk of a corpse, the halakha is that if there is a handbreadth of space between the corpse and the roof, the roof serves as a barrier that prevents the ritual impurity from spreading beyond the roof. However, if there is less than a handbreadth of space between the corpse and the roof, the roof does not serve as a barrier, and the ritual impurity spreads upward. In a house of that sort where one filled the space between the corpse and the roof with straw or pebbles mixed with clods of dirt, and then nullified the straw or dirt, it is effectively nullified, and the ritual impurity spreads upward.