יורה דעה קצ״חYoreh De'ah 198

Se’if 1א׳

צְרִיכָה שֶׁתִּטְבֹּל כָּל גּוּפָהּ בְּפַעַם אַחַת; לְפִיכָךְ צָרִיךְ שֶׁלֹּא יִהְיֶה עָלֶיהָ שׁוּם דָּבָר הַחוֹצֵץ. וַאֲפִלּוּ כָּל שֶׁהוּא, אִם דֶּרֶךְ בְּנֵי אָדָם לִפְעָמִים לְהַקְפִּיד עָלָיו, חוֹצֵץ אֲפִלּוּ אִם אֵינָהּ מַקְפֶּדֶת עָלָיו עַתָּה, אוֹ אֲפִלּוּ אֵינָהּ מַקְפֶּדֶת עָלָיו לְעוֹלָם כֵּיוָן שֶׁדֶּרֶךְ רֹב בְּנֵי אָדָם לְהַקְפִּיד עָלָיו, חוֹצֵץ; וְאִם הוּא חוֹפֶה רֹב הַגּוּף, אֲפִלּוּ אֵין דֶּרֶךְ בְּנֵי אָדָם לְהַקְפִּיד בְּכָךְ, חוֹצֵץ. הַגָּה: וּלְכַתְּחִלָּה לֹא תִּטְבֹּל אֲפִלּוּ בִּדְבָרִים שֶׁאֵינָם חוֹצְצִין, גְּזֵרָה אָטוּ דְּבָרִים הַחוֹצְצִים (הַגָּהוֹת ש"ד).

She must immerse her whole body at one time; therefore there must not be upon her any thing that interposes. And even the least amount at all: if it is the way of people sometimes to be particular about it, it interposes — even if she is not particular about it now, or even if she is never particular about it, since it is the way of most people to be particular about it, it interposes. And if it covers the greater part of the body, even though it is not the way of people to be particular in such a case, it interposes. Hagah [Rema]: And at the outset she shall not immerse even with things that do not interpose, a decree on account of the things that do interpose. (Hagahot Shaarei Dura)

Se’if 2ב׳

אֵלּוּ הַדְּבָרִים שֶׁחוֹצְצִין, חוּטֵי צֶמֶר וְחוּטֵי פִּשְׁתָּן וּרְצוּעוֹת שֶׁכּוֹרְכִין בָּהֶם הַשֵּׂעָר בָּרֹאשׁ, לֹא תִּטְבֹּל בָּהֶם עַד שֶּׁתְּרַפֵּם; וְאִם הֵם בְּתוֹךְ קְלִיעַת שַׂעֲרָהּ אֵינוֹ מוֹעִיל בָּהֶם רִפְיוֹן. וְאִם הֵם כְּרוּכִים בִּשְׁאָר מְקוֹמוֹת בַּגּוּף, לֹא תִּטְבֹּל בָּהֶם עַד שֶּׁתְּרַפֵּם, חוּץ מֵאִם הֵם כְּרוּכִים בַּצַּוָּאר שֶׁאֵינָם חוֹצְצִין לְפִי שֶׁאֵינָהּ מְהַדְּקָן; אֲבָל קָטְלָא, שֶׁהִיא רְצוּעָה חֲלָקָה וּרְחָבָה שֶׁכּוֹרֶכֶת סְבִיב צַוָּארָהּ, חוֹצֶצֶת, מִפְּנֵי שֶׁחוֹנֶקֶת עַצְמָהּ בְּחֹזֶק, כְּדֵי שֶׁיִּהְיֶה בְּשָׂרָה בּוֹלֵט וְתֵרָאֶה בַּעֲלַת בָּשָׂר, וּמִתּוֹךְ שֶׁהָרְצוּעָה חֲלָקָה וּרְחָבָה אֵינָהּ מַזִּיקָתָהּ (רַשִׁ"י).

These are the things that interpose: threads of wool and threads of flax, and the straps with which they bind the hair on the head — she shall not immerse in them until she loosens them; and if they are within the plaiting of her hair, loosening does not avail for them. And if they are wound about the rest of the places on the body, she shall not immerse in them until she loosens them, except where they are wound about the neck, for they do not interpose, since she does not draw them tight. But a katla, which is a smooth broad strap that she winds about her neck, interposes, because she chokes herself with it forcefully so that her flesh should protrude and she be seen as a fleshy woman; and since the strap is smooth and broad it does not hurt her. (Rashi)

Se’if 3ג׳

אִם הַחוּטִין הָאֵלּוּ חֲלוּלִין, עֲשׂוּיִן מַעֲשֵׂה רֶשֶׁת, אֵינָם חוֹצְצִין (טוּר בְּשֵׁם רַאֲבָ"ד).

If these threads are hollow, made in the manner of a net, they do not interpose. (Tur in the name of the Raavad)