To make a garment of wool or linen, the raw materials must undergo three stages alluded to in the word sha’atnez, as the Mishna explains: “Sha’atnez: something that is shua, tavui, and nuz” (Mishna, Kilayim 9:8). First, shua: smoothing the wool or flax by combing. Second, tavui: spinning the fibers into thread. Third, nuz: intertwining, whether by weaving wool and linen threads together as warp and weft to form cloth, or by joining linen thread to a wool garment through tying or sewing.
In practice, wool and linen form prohibited sha’atnez in four principal ways: when raw wool and flax fibers are blended, combed, spun together into thread, and woven into cloth; when wool and linen threads are produced separately and then woven into a single fabric, such as linen warp and wool weft; when wool fabric is sewn or tied with linen thread, or linen fabric with wool thread; and when wool and linen fabrics are sewn together.
What these cases have in common is that the wool and linen underwent all three stages of shua, tavui, and nuz. If they did not undergo all three stages, however, as with felt made by compressing raw wool or flax without spinning or weaving, the overwhelming majority of Rishonim maintain that joining them is not prohibited by Torah law. Rambam disagrees and maintains that even wool and flax that underwent only the first stage of smoothing and combing before being made into felt are prohibited by Torah law when joined.[3]
[3]. There are four approaches to defining the Torah prohibition of sha’atnez.
- a) According to Rashi, the Torah prohibition applies only when the wool and flax undergo all three stages together: shua, tavui, and nuz – smoothing, spinning, and weaving. This is also the view of Rivan, Ra’avan, Shibolei ha-Leket, and others. This view appears difficult in light of the Gemara’s statement that tying woolen tzitzit to a linen garment constitutes sha’atnez by Torah law (Yevamot 4a), even though the wool and linen were not processed together. R. Eliyahu Mizraḥi explains that all three stages must be performed together only when wool and flax are woven into a single fabric and can no longer be distinguished from one another. When each material remains distinct – as in a wool fabric joined to a linen fabric, or woolen tzitzit tied to a linen garment – sewing or tying them together violates Torah law. Meiri offers another explanation: because a knot creates a particularly strong bond, it joins the wool and flax even though they did not undergo the three stages together.
- b) According to Rabbeinu Tam, Ramban, Rosh, Rashba, Ritva, Semag, Semak, Yere’im, Ran, Peraḥ Shoshan, and others, even if the wool and linen threads were produced separately, weaving them together or joining them by sewing or tying is prohibited by Torah law. This applies only if each thread is plied, meaning that it consists of at least two strands twisted together, since they understand nuz to mean plying. If the threads are unplied, the prohibition is rabbinic. Whether the modern process of roving (mezira) qualifies as plying requires further study.
- c) R. Shimshon of Sens accepts all the cases prohibited by Rashi and Rabbeinu Tam but extends the Torah prohibition further: even unplied wool and linen threads are prohibited by Torah law when woven together, sewn together, or tied to one another. In his view, nuz includes any winding together of the materials – thread around thread or thread around fabric. R. Yeruḥam cites this view in the name of Ramah, and it is also the position of Or Zaru’a and Tashbetz. Many Aḥaronim take this view into account (Sefer ha-Zikhronot 3; Ginat Veradim, YD 6:13; Tzemaḥ Tzedek, YD §353). This is the approach presented above.
- d) According to Rambam, combining wool and flax that have undergone only smoothing, without spinning or weaving, is prohibited by Torah law. This is also the view of R. Ḥananel, following Rav Ashi (Nidda 61b). Most Rishonim, however, maintain that combining wool and linen felt is prohibited only rabbinically, since the fibers have not undergone all three stages of smoothing, spinning, and intertwining, following Mar Zutra in the same passage. This is the view of Rav Hai Gaon, Rav Sherira Gaon, and all the Rishonim cited in the preceding approaches. There are also several other explanations of Rambam’s position.
