There is a common misconception that laws of Shatnez (mixing wool and linen) is not applicable today either because it does not exist in our current clothing or because it is no longer practiced. This is absolutely incorrect. This biblical commandment and mitzvah is still very much in force today and common in contemporary clothing styles.  Surprisingly, the mixing of wool and linen in mass-produced clothing is much more prevalent than you would think.

 
What is Shatnez?
 
The Torah prohibits wearing a mixture of wool and linen in the same piece of clothing, as it is written, "You shall not wear combined fibers, wool and linen together" (Deut. 22:11). In Hebrew, this forbidden mixture, called Shatnez, is an acronym for different forms in which it may occur: combed (shua), spun (tovi) and woven (nooz). Each describes the various stages in processing fabric: combing the raw fiber, spinning fibers into a thread, and weaving the threads into cloth. Wool and linen attached to each other by any other means (glue, staple, sewn, velcro etc.) is forbidden by Rabbinical Law. The prohibition of Shatnez applies to any sort of garment, whether it is worn as socks, shoes, gloves, pajamas, etc., and wore for any period of time, no matter how brief. It is forbidden to wear any garment until thread of either wool or linen is removed.


What Needs To Be Checked? How Do We Check?
 
In general, clothes that list with wool or linen on the label should be taken to a certified shatnez checker, where under a microscope the fibers in the garment are examined. Even though only one of the two forbidden fibers is listed, the odds of finding shatnez is fairly great. Manufacturers are not required by law to reveal every element in their clothing and even the smallest amount of Shatnez is forbidden. Even if a garment says 100 percent wool, it may legally still contain linen threads. For example, some woolen suits buttons are sewn with linen thread. Garments are usually (but not always) safe from shatnez if neither linen nor wool are mentioned on the label.

However, regardless of their labels, men's and women’s suits and coats should always be checked for Shatnez because their sophisticated construction can often include Shatnez. Once Shatnez is found, in most cases, the Shatnez fibers can be easily removed as the wool and linen are not combined in the basic fabric of the garment. Once removed, garment can be worn without any problems. Whenever one is in doubt if a garment needs to be tested, a certified Shatnez Checker should be consulted.

The most common case of shatnez is in the collar of men's suits and coats. To retain the shape of the collar area, a canvas stiffener is generally sewn into the collar, and linen is the fabric considered by the clothing industry as being the best material for this purpose. This linen collar can then easily be removed and replaced with a non-linen canvas. Often, the more expensive the suit, the greater the likelihood that linen may be used.

Rabbi Avraham Danzig, in his Chochmat Adam (Hilchot Shatnez 106:28) writes that “anyone who is careful to avoid wearing shatnez will merit to be dressed in garments of salvation and a cloak of righteousness."