This Halacha is an excerpt from our Sefer
Buy me here or on Amazon.com
Kefulos and Nefuchos:
The following stringencies regarding Matzah are accustomed amongst Ashkenazi Jewry, to suspect for Chametz, even though they do not have any Talmudic source. One must abide by this custom.
Kefula: A Kefula is when a Matzah contains a fold which is touching on both ends without any interval of air in-between the fold and the Matzah. If one finds such a fold on his Matzah, then one must remove the folded area and the worth of a thumbs width that surrounds the area of the fold. If this fold was found on Pesach, from the 5th hour of Erev Pesach and onwards, it is proper to be stringent to burn this area of Matzah that must be removed. If the fold is not touching the Matzah at both ends, even if there is only a tiny space of air in-between them, the Matzah is Kosher, unless one sees that the area under the fold has not changed color. If the Kefula area of the Matzah became mixed with other food, there is no need to be stringent and forbid the mixture. If one discovered the Kefula in one’s Matzah after Pesach, it is permitted to be eaten.
Nefucha: A Nefucha is if there is a hollow vacuum with an air bubble the size of an average thumb top, on the Matzah. If a Nefucha of this size was discovered on the Matzah, the entire Matzah is forbidden to be eaten, as the air bubble reveals that the entire Matzah is Chametz. [Practically, the custom today regarding our Matzahs which are very thin and cracker like, is to permit eating Matzahs that contain Nefuchos air bubbles, and hence they may even initially be eaten on Pesach. However, regarding Kefulos, one must be stringent even regarding Matzahs of today.]
 Admur 461:16-28; Rama 461:5; Terumos Hadeshen 127
 Admur 461:27
 Admur 461:16
The reason: As we suspect that the area in between the fold did not bake very well, and has hence become Chametz. [Admur ibid]
 Admur 461:21
The reason: It is not an obligation to destroy being that the Matzah only contains a suspicion of Chametz, and is not actual Chametz. Nonetheless, it is proper to do so. [Admur ibid]
 Admur 461:22
 Admur 461:27
 Admur 461:29
 Admur 461:23-27; Rama 461:5; Maharil p. 77
 Admur 461:25
 Shaareiy Teshuvah 461:15 in name of Dvar Shmuel 234; Ashel Avraham Butchach 461; M”B 461:10; Piskeiy Teshuvos 461:10
 See Admur 500:18
 Once the piece is in one’s hand it may be discarded. However, if one put it down, it is now Muktzah and may no longer be moved.