סימן ט סעיף יב
סְתָם צֶמֶר הָאָמוּר בַּתּוֹרָה וּבַפּוֹסְקִים, הוּא צֶמֶר רְחֵלִים וְאֵילִים. וְטַלִּית שֶׁהַשְּׁתִי הוּא שֶׁל צֶמֶר וְהָעֵרֶב הוּא שֶׁל צֶמֶר גֶּפֶן אוֹ מֶשִׁי וְכַדּוֹמֶה אוֹ לְהִפּוּךְ שֶׁהָעֵרֶב הוּא שֶׁל צֶמֶר וְהַשְּׁתִי הוּא מִמִּין אַחֵר, יְרֵא שָׁמַיִם לֹא יְבָרֵךְ עַל טַלִּית כָּזֶה, מִשׁוּם דְּיֵשׁ אוֹמְרִים דְּגַם צִיצִית שֶׁל צֶמֶר אֵינָן פּוֹטְרִין רַק בֶּגֶד שֶׁהוּא מִמִּינָן. וְכֵן טַלִּית שֶׁל מֶשִׁי וְהַצִּיצִית הֵן שֶׁל צֶמֶר, לֹא יְבָרֵךְ עָלָיו, אֶלָּא יְבָרֵךְ תְּחִלָּה עַל טַלִּית שֶׁל צֶמֶר וְיִתְעַטֵּף בּוֹ וְאַחַר כָּךְ יְסִירוֹ וְיִתְעַטֵּף בָּזֶה. אַךְ אִם גַּם הַצִּיצִית הֵן שֶׁל מֶשִׁי, יְכוֹלִין לְבָרֵךְ עָלָיו. (וְלָא שְׁכִיחֵי בִּמְדִינָתֵנוּ צִיצִית שֶׁל מֶשִׁי דְהָא צִיצִית בָּעֵינָן טְוִיָּה לִשְׁמָהּ). וְאִם מִקְצָת צִיצִית שֶׁל מֶשִׁי וּמִקְצָתָן שֶׁל צֶמֶר, גָּרוּעַ טָפֵי, וְאֵין לַעֲשׂוֹת כֵּן (סִימָן ט).
When the Torah refers to "wool" or when the Poskim do so they [usually mean] sheep's or ram's wool. A pious person should not recite the berachah over a tallis [in which] the warp [threads] are made of wool and the woof threads are made of cotton, silk or the like; or the reverse, [that is,] that the woof threads are made of wool and the warp threads are of another material, because some Poskim maintain that even tzitzis made of wool only exempt a garment made of the same material.38The tzitzis must be made of the same material as the garment.There are opinions, however, that tzitzis made of wool exempt “any” garment. Since this ruling is not universally accepted we refrain from reciting a berachah. Similarly, over a tallis made of silk and the tzitzis are made of wool, a berachah is not said, but, [rather,] you should first recite the berachah over a woolen tallis and enwrap yourself with it and remove it (the woolen tallis), and then, enwrap yourself with it (the silk tallis).39By making a berachah over the woolen tallis and having in mind to exempt the silk tallis, he removes any controversy from his actions. However, if the tzitzis [of the silk tallis] were also made of silk you may recite a berachah over it (the tallis,)40All authorities agree that where the garment and the tzitzis are made of the same material, the berachah may be said. (Tzitzis of silk are not common in our countries because tzitzis must be spun for the purpose of tzitzis).41Lit. for its sake, i.e., for the sake and purpose of fulfilling the mitzvah. This intent must be stated verbally at the time of the spinning. If the tzitzis were partially made of silk and partially of wool it is even worse (more questionable) and (tzitzis) should not be made in this manner.42It has become customary to attach wool tzitzis to silk garments and a berachah may be said (Mishnah Berurah 9:6). [Note: Shulchan Aruch 7:4 rules that leather garments are exempt from tzitzis because only woven garments are obligated to have tzitzis. Accordingly, nylon garments are exempt from tzitzis (Igros Moshevol. II, 2).] Rav Z.P. Frank in Har Tzevi maintains that nylon garments do require tzitzis.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)