3,103. The Minimum Volume for Shaatnez

Hilchos Kilayim 10:4

How do we know that all of the aforementioned are Biblical prohibitions? The Torah needs to explicitly permit mixed fabrics in tzitzis. The Oral Law teaches that the section prohibiting mixed fabrics is juxtaposed with the section regarding tzitzis specifically to teach that mixed fabrics are permitted in tzitzis, which are strings tied together. We therefore infer that such a connection when it does not involve a mitzvah is prohibited under Biblical law; the Torah would have no need to exclude something that would only later be prohibited by rabbinic enactment.

Hilchos Kilayim 10:5

There is no minimum volume when it comes to mixed fabrics. Even the smallest wool thread in a large linen garment – or vice versa – is prohibited.