Parshas Ki Setzei
“You shall not wear Sha’atnez, wool and linen together!” (Devarim 22:11)
It is a negative commandment that we may not wear clothing which is made up of wool and linen joined together. This is called Sha’atnez. About this it says “You shall not wear Sha’atnez, wool and linen together!”.
Amongst the roots of this commandment is that which the Rambam writes that it is because the priests who served the idols in those days used to wear these clothes. He writes further that even nowadays (in his days) this is a well-known fact amongst Egyptian priests.
Amongst the laws of this commandment are that the biblical prohibition only applies when it is “Shua, Tovuy and Noz”. This means that the wool has been combed, spun and twisted into thread by itself and the linen has also has been combed, spun and twisted into thread by itself, and afterwards they were joined together, either by weaving or even by tying (so long as there are at least two knots). In this case it is biblical Sha’atnez. However, if the above three things have not been done to it then it is only rabbinical Sha’atnez and not biblical. Chazal said that even if there are ten blankets on top of each other and there is Sha’atnez underneath them, one may not sit on them.
This prohibition applies in all places and at all times both to men and to women.