|Halakhic texts relating to this article|
|Torah:||Leviticus 19:19 and Deuteronomy 22:11|
|Jerusalem Talmud:||Tractate Kil'ayim (chapter 9)|
|Mishneh Torah:||Hilchos Kilayim 10|
|Shulchan Aruch:||Yoreh De'ah, 298–304|
Shatnez (or shaatnez, [ʃaʕatˈnez]; Biblical Hebrew Šaʿatnez שַׁעַטְנֵז (help·info)) is cloth containing both wool and linen (linsey-woolsey), which Jewish law, derived from the Torah, prohibits wearing. The relevant biblical verses (Leviticus 19:19 and Deuteronomy 22:11) prohibit an individual from wearing wool and linen fabrics in one garment, the blending of different species of animals, and the planting together of different kinds of seeds (collectively known as kilayim).
The word is not of Hebrew origin, and its etymology is obscure. Wilhelm Gesenius's Hebrew Dictionary cites suggestions that derive it from Semitic origins, and others that suggest Coptic origin, finding neither convincing. The Septuagint translates the term as κίβδηλον, meaning 'adulterated'.
The Modern Hebrew word שעטנז means 'mixture'.
Early writers, like Maimonides, state that the prohibition was a case of the general law (Leviticus 20:23) against imitating Canaanite customs. Maimonides wrote: "the heathen priests adorned themselves with garments containing vegetable and animal materials, while they held in their hand a seal of mineral. This you will find written in their books". Classical Kabbalah regarded such combinations as a defiance of God, because according to them, God had given each species individuality.
Because the priest's girdle, and the tzitzit which every man wore, are preferably made from shatnez, the prohibition was a way of setting aside this fiber blend only for holy purposes.
According to modern biblical scholars (and Josephus), the rules against these mixtures are survivals of the clothing of the ancient Jewish temple and that these mixtures were considered to be holy and/or were forfeited to a sanctuary. It may also be observed that linen is a product of a riverine agricultural economy, such as that of the Nile Valley, while wool is a product of a desert, pastoral economy, such as that of the Hebrew tribes. Mixing the two together symbolically mixes Egypt and the Hebrews. It also violates a more general aversion to the mixing of categories found in the Leviticus holiness code, as suggested by anthropologists such as Mary Douglas.
Rabbi Abraham Isaac Kook suggested that shearing wool from sheep is, at some level, "a form of theft, the oppression of the weak at the hands of the strong." Since utilizing the flax plant and sheep are not – in absolute terms – morally equivalent, the Torah sought to distinguish between them, to instill a sensitivity towards animal welfare. 
Limitations of the law
Definition of shatnez material
In the Torah, one is prohibited from wearing shatnez only after it has been carded, woven, and twisted, but the rabbis prohibit it if it has been subjected to any one of these operations. Hence felt made with a mixture of wool compressed together with linen is forbidden. Silk, which resembled wool, and hemp, which resembled linen, were formerly forbidden for appearance's sake, but were later permitted in combination with either wool or linen because they are now distinguishable. Hempen thread was thus manufactured and permitted for use in sewing woolen clothing.
Only sheep's wool is considered as wool, the finest being that of lambs and rams; excluded is camels' hair, the fur of hares, and the wool of goats. If any of the excluded wools is mixed with sheep's wool, or spun with it into thread, the character of the material is determined by the proportion of each. If the greater part of it is sheep's wool, it is reckoned as wool; if the contrary, it is not wool and may be mixed again with linen.
Rabbinic Judaism maintains that shatnez was permitted in the case of the avnet (Kohen's girdle), in which fine white linen was interwoven with purple, blue, and scarlet material. According to the rabbis, the purple, blue, and scarlet were made from wool and interwoven with the fine linen.
Karaite Judaism maintains that the purple, blue, and scarlet materials must also have been made of linen, since the Torah prohibits wearing garments made from combinations of wool and linen. The Torah does not state from what materials the purple, blue, and scarlet threads were made.
The phrase regarding the kohanim sons of Zadok, "they shall not gird themselves with any thing that causeth sweat" is interpreted in the Talmud to mean "they shall not gird themselves around the bent of the body, where sweat effuses most". Rabbi Judah haNasi was of the opinion that the girdle of the ordinary priest was of shatnez, but Rebbi Eleazar says it was of fine linen. The Talmud states that the high priest wore a linen girdle on Yom Kippur and a girdle of shatnez on all other days.
Torah law forbids kil'ayim (shatnez) - "intertying" wool and linen together, with the two exceptions being garments of kohanim[further explanation needed] and tzitit. Concerning tzitzit, chazal permit using wool and linen strings in tandem only when genuine tchelet or tekhelet is available, whereas kabbalist sources take it a step further by encouraging its practice.
Contact with shatnez
The Talmud argues that a woolen garment may be worn over a linen garment, or vice versa, but they may not be knotted or sewed together. Shatnez is prohibited only when worn as an ordinary garment, for the protection or benefit of the body, or for its warmth, but not if carried on the back as a burden or as merchandise. Felt soles with heels are also permitted, because they are stiff and do not warm the feet. In later times, rabbis liberalised the law, and, for example, permitted shatnez to be used in stiff hats.
Cushions, pillows, and tapestry with which the bare body does not touch do not come under the prohibition, and lying on shatnez is technically permitted. However, classical rabbinical commentators feared that some part of a shatnez fabric might fold over and touch part of the body; hence, they went to the extreme of declaring that even if only the lowest of 10 couch-covers is of shatnez, one may not lie on them.
Observance and enforcement of the shatnez law
Many people bring clothing to special experts who are employed to detect the presence of shatnez. A linen admixture can be detected during the process of dyeing cloth, as wool absorbs dye more readily than linen does. Wool can be distinguished from linen by four tests—feeling, burning, tasting, and smelling; linen burns in a flame, while wool singes and creates an unpleasant odor. Linen thread has a gummy consistency if chewed, due to its pectin content; a quality only found in bast fibers.
Observance of the laws concerning shatnez became neglected in the 16th century, and the Council of Four Lands found it necessary to enact (1607) a takkanah ("decree") against shatnez, especially warning women not to sew woolen trails to linen dresses, nor to sew a velvet strip in front of the dress, as velvet had a linen back.
Observant Jews in current times also follow the laws of shatnez, and newly purchased garments are checked by experts to ensure no forbidden admixtures are used. In addition to the above-mentioned methods, modern shatnez experts employ the use of microscopy to determine textile content. In most cases, garments that do not comply can be made compliant by removing the sections containing linen. Some companies label compliant products with "shatnez-free" tags.
Karaites and shatnez
Karaite Jews, who do not recognize the Talmud, forbid the wearing of garments made with linen and wool (and fibers from any plant and/or any animal) at once under any circumstances. It is forbidden even for one to touch the other.
- Maimonides, Moreh, 3:37
- Peake's commentary on the Bible
- Josephus. Antiquities 4:8:11.
- Morrison, Chanan; Kook, Abraham Isaac Kook (2006). Gold from the Land of Israel: A New Light on the Weekly Torah Portion - From the Writings of Rabbi Abraham Isaac HaKohen Kook'. Urim Publications. p. 201. ISBN 965-7108-92-6.
- Talmud, Tractate Niddah 61b
- Tractate Kilaim ix. 9
- talmud, Tractate Kilaim ix. 3
- cf. 2 Kings 3:4
- Talmud, Tractate Kilaim ix. 1
- Exodus 28:6
- Ezekiel 44:18
- Talmud, Tractate Zebachim. 18b
- Talmud, Tractate Yoma 12b
- "Tzitzit made of kilayim? –". Kehuna.org. 2014-04-23. Retrieved 2019-06-11.
- Sifra, Deuteronomy 232
- Talmud, Tractate Betzah 15a
- Sefer ha-Chinuch, section "Ki Tetze", No. 571
- Talmud, Tractate Kilaim. ix. 2
- Talmud, Tractate Yoma 69a
- Ha-Karmel, i., No. 40
- Gratz, Gesch. vii. 36, Hebrew ed., Warsaw, 1899
- Maimonides. Mishneh Torah, Kilayim, x.;
- Ṭur Yoreh De'ah;
- Shulkhan Arukh, Yoreh De'ah, 298–304;
- Israel Lipschitz, Batte Kilayim. Appended to his commentary on the Mishnah, section Zera'im: Ha-* Maggid (1864), viii., Nos. 20, 35;
- M. M. Saler, Yalḳuṭ Yiẓḥaḳ ii. 48a, Warsaw, 1899.
- Holy Bible, New International Version®, NIV® Copyright © 1973, 1978, 1984, 2011