Leviticus 19:19 states that it is forbidden to wear shatnez—a mixture of wool and linen. In the words of the Torah: “You shall observe My statutes: . . . and a garment which has a mixture of shatnez shall not come upon you.” (This mitzvah is also mentioned in Deuteronomy 22:11.)

The reason for this prohibition is not clear. As the verse says: “You shall observe My statutes . . .” This means that this mitzvah is a chok—a divine statute that defies (full) comprehension. Nevertheless, the commentaries attempt to somewhat explain this mitzvah. Maimonides says that shatnez garments were worn by idolatrous priests, and we are forbidden from following in their ways.1 Others say that mixing wool and linen is akin to mixing, and unleashing, the spiritual forces associated respectively with Cain and Abel, and can have damaging results. (Cain brought a sacrifice of flax, from which linen is made; Abel sacrificed sheep, producers of wool.)2

Some of the laws governing the observance of this mitzvah are:

  1. Even if linen threads were used to sew buttons onto a wool suit, or to reinforce shoulder padsShatnez is forbidden whether the mixture of wool and linen occurred at the stage of combing, spinning or weaving. Even if linen threads were used to sew buttons onto a wool suit, or to reinforce shoulder pads, this is forbidden as shatnez.3
  2. If purchasing a suit that contains either wool or linen, you should have the garment inspected by a shatnez expert, to establish that it does not contain shatnez. These experts take appropriate samples from the garment (without ruining the garment) and send the samples to a shatnez laboratory. At the laboratory, the sample is examined under a low-powered microscope, and the materials are identified.
  3. According to experts in the field, even if the label says that the garment is 100% wool, it may possibly contains shatnez. A label that states that a garment is 100% wool may contain as much as 2% of other materials. In addition, the label describes only the shell of the garment, and not the padding and ornamental threads. For more on this topic, see The Mysterious World of Shatnez.
  4. In these matters, one may trust only a Jew who is observant of the shatnez laws and who is specially trained in this field.4
  5. One may try on a suit to see if it fits, despite the fact that it may contain shatnez.5
  6. One may wear a woolen jacket over a linen shirt, or vice versa, as long as it is possible to take off one without taking off the other.6
  7. The prohibition of shatnez extends to all types of materials, including soft curtains, tablecloths and towels.7