Shatnez is a prohibition from the Torah. It is a Mitzvas Lo Saseh (negative commandment) meaning you fulfill this obligation by refraining from doing an action. (In this case it is refraining from wearing, or draping on oneself a garment or fabric containing a forbidden mixture of wool and linen). 

There are two verses in the Torah that refer to shatnez. One in Vayikra 19:19, “Ubeged kilayim shatnez lo ya’aleh alecha.” A garment composed of a shatnez mixture should not cover you. And in Devarim 22:11 another expression of this same mitzvah, “Lo silbash shatnez tzemer uphishtim yachdav.” Do not wear shatnez, wool and linen together. The prohibition of shatnez is with wool and linen only. A garment made from any other combination of fibers is permitted to wear.

Shatnez is classified as a form of Kilayim (forbidden mixture of the Torah). There are 4 forms of Kilayim mentioned in the Torah Kilyam of animals, Kilyam of the vineyard, Kilyam of plants and Kilyam of clothes which is also called shatnez.

Our Sages teach us the word shatnez  (שעטנז)is actually an acronym of the words שוע טווי נוז to teach us that the combination is prohibited only if the wool and linen fibers have been combed, spun and woven or twined.

The wool referred to here is specifically wool, the hair, which comes from a sheep or lamb. Other forms of wool such as cashmere which comes from a goat may be combined with linen. Likewise the linen referred to in the Torah is specifically that which comes from the flax plant.  Cotton or ramie or any plant fiber that is similar to linen may be combined with wool. It is only when sheep’s wool is joined with linen is the resulting combination shatnez. This is implied by the word yachdav –together.

If even a single thread of linen and wool have been joined together, whether in a cloth or garment it is a forbidden shatnez combination.

Wool and linen are shatnez if they are attached together in any lasting manner not just through sewing but also by bonding, gluing or tying for example.

Wool and linen garments attached together via buttons, or Velcro are permitted even if left like that on a permanent basis.   This is not considered an attachment because the garments can be easily unfastened. It would therefore, be permitted to wear a raincoat containing linen, together with a buttoned in wool lining.

Regarding zippers, there is a difference of opinions.  Some authorities consider a zipper as a form of permanent attachment and would prohibit a zippered in lining. Others maintain that this too, is similar to buttons due to the ease of removal and is, therefore, permitted.

There is no minimum measurement of shatnez even the smallest thread of linen joined to a wool article or vise versa will make the entire garment shatnez.

Furthermore, the shatnez is not required to be an essential part of the garment. For example if a label in a wool suit or a hanger loop in a wool skirt was sewn in with a linen thread the entire garment is forbidden to wear.

That being said it is possible to have shatnez nullified within the fibers of a thread containing other fiber(s) other then wool or linen. For example a thread containing a blend of cotton and linen; if the cotton is the majority it may be permitted to sew it together with wool. If the linen is 50% or more then it is forbidden as shatnez. Similarly  a thread spun of wool and cashmere; if the majority fiber is cashmere the thread would be permissible with linen. If 50% or more of the fiber in the thread is wool then it is forbidden with linen.

Wool and linen fiber can never be nullified one within the other.

Only a highly qualified shatnez tester is capable of determining the accurate percentages of textile fibers within a thread.

A shatnez garment is forbidden to wear even if the garment is not touching one’s body, even if separated by many layers of clothing.

A small area of shatnez forbids the entire garment. For example; a neutral material such as cotton or polyester will be entirely forbidden if a wool and linen combination are sewn on to even a small corner of the garment. Even if a person lets the part of the garment that contains the shatnez lie on the floor and only wraps himself in the neutral part this is also forbidden as shatnez.

A garment made from a neutral material has on one end sewn threads of wool and on the other far end threads of linen, even though the wool and linen are not touching one another according to the Rambam this is forbidden from the Torah as shatnez and according to the Rama’ it is permitted.

The prohibition of shatnez applies equally to men and woman. Shatnez is forbidden at all times.

The prohibition of shatnez applies irrespective of whether the garment is one’s own, borrowed or rented.

Shatnez is forbidden to be worn for even for a short time or on a temporary basis. Each moment a person is wearing shatnez he is transgressing the prohibition anew.

If you have questions regarding shatnez, you may write to Rabbi Neiman at [email protected]

Rabbi Eliyahu Neiman in 1991 was certified as expert in the field of shatnez in testing and halacha from the “Vaad Mishmeres Habeged” of Bnei Brak and the “International Association of Professional Shatnez Testers and Laboratories” of  Lakewood, NJ. 
Founded and managed the “Kiryat Sefer-Modi’in Illit Shatnez Laboratory from 1991-2005.
Senior tester in “Mishmeres Nasson Shatnez Laboratories Jerusalem from 2002-2008.
Rabbi Neiman is presently manager of the “Shatnez Express Betar Illit” as well as the “RBS (Ramat Beit Shemesh) Shatnez Laboratory”. He also runs Shatnez pick-ups in Jerusalem’s Ramat Eshkol, Yeshiva Ohr Somayach and N’vei Yaakov.

(Jerusalem Kosher News – www.jerusalemkoshernews.com)