TT #732 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:09
Then his yevamah shall approach him in the presence of the elders, and draw his shoe off his foot, and spit in his face, and respond and say: “Thus shall be done to the man who will not build up his brother’s house.”
Torah Temimah points to Yevamot 101a.
TT lemma: וְחָלְצָה נַעֲלוֹ.
חָלְצָה בְּאַנְפִּלְיָא – חֲלִיצָתָהּ פְּסוּלָה; מַאי טַעְמָא? מִידֵּי דְּמָגֵין בָּעֵינַן, דִּכְתִיב נַעַל.
English: If she performed chalitzah with a soft cloth shoe (anpilya) — her chalitzah is invalid; why? We require something that protects, for it is written “shoe.”
On the daf / in context: Only a proper protective shoe (of leather) qualifies for the rite.
Derash defining a valid shoe.
Chalitzah performed with a non-protective cloth shoe is invalid.