כלאים ט׳Kilayim 9

Mishnah 1א׳

אֵין אָסוּר מִשּׁוּם כִּלְאַיִם אֶלָּא צֶמֶר וּפִשְׁתִּים. וְאֵינוֹ מִטַּמֵּא בִנְגָעִים אֶלָּא צֶמֶר וּפִשְׁתִּים. אֵין הַכֹּהֲנִים לוֹבְשִׁין לְשַׁמֵּשׁ בְּבֵית הַמִּקְדָּשׁ אֶלָּא צֶמֶר וּפִשְׁתִּים. צֶמֶר גְּמַלִּים וְצֶמֶר רְחֵלִים שֶׁטְּרָפָן זֶה בָזֶה, אִם רֹב מִן הַגְּמַלִּים, מֻתָּר, וְאִם רֹב מִן הָרְחֵלִים, אָסוּר. מֶחֱצָה לְמֶחֱצָה, אָסוּר. וְכֵן הַפִּשְׁתָּן וְהַקַּנְבּוֹס שֶׁטְּרָפָן זֶה בָזֶה:

The prohibition of kilayim [the product of forbidden crossbreeding or working of certain animals with one another, planting together certain plants, or interweaving certain fibers] applies only to [sheep's] wool and linen, and only wool and linen can become unclean by negaim [diseased patches on skin, clothes, or houses that create impurity]. The priests, while in the service in the Temple only wear [garments] of wool and linen. Camel's wool and sheep's wool that have been mixed together, if the majority [of the wool] is from the camel, it is permitted [to mix them with linen, since the minority is annuled by the majority]. If the majority is from the sheep, it is forbidden [to mix them with linen]. If they are half and half [equal amounts], they are forbidden. The same [rule] applies to hemp and flax that have been mixed together.

Mishnah 2ב׳

הַשִּׁירָיִים וְהַכָּלָךְ אֵין בָּהֶם מִשּׁוּם כִּלְאַיִם, אֲבָל אֲסוּרִים מִפְּנֵי מַרְאִית הָעָיִן. הַכָּרִים וְהַכְּסָתוֹת אֵין בָּהֶם מִשּׁוּם כִּלְאַיִם, וּבִלְבַד שֶׁלֹּא יִהְיֶה בְשָׂרוֹ נוֹגֵעַ בָּהֶן. אֵין עֲרַאי לְכִלְאָיִם. וְלֹא יִלְבַּשׁ כִּלְאַיִם אֲפִלּוּ עַל גַּבֵּי עֲשָׂרָה, אֲפִלּוּ לִגְנֹב אֶת הַמֶּכֶס:

Shirayim [type of silk which resembles linen] and kolach [a type of silk which resembles wool], are not subject to the laws of kilayim, but are [nevertheless] forbidden due to mar'it ha'ayin [an action or situation which might be misinterpreted by the casual viewer, who might think it involves a transgression where there is none, or come to permit forbidden actions based on what he has seen]. Mattresses and pillows are not subject to the laws of kilayim [by laying on them], provided one's flesh do not touch them. There is no [exemption for the] temporary wearing of kilayim and one may not wear kilayim even on top of ten [other garments], even if it only to evade paying customs.