Hasidic men and women walk through a Jewish Orthodox neighborhood in Brooklyn on April 24, 2017 in New York City.

How Orthodox Jews Observe The Commandment To Not Wear Wool And Linen Together

The concept of kosher food is widely known, but what about kosher clothing? It’s a big issue too, though you might not be aware of it.

In the Orthodox Jewish community, what you wear is just as important as what you eat — and it’s all got to be certified by an authority beforehand. In fact, for those who observe the practice, even before yanking the store tags off new clothing, buttoning up thrift store finds, or slipping into that hand-me-down 1950’s dress coat from Bubbe, the majority of those garments are brought or sent by mail to a local laboratory and tested for shatnez — a blend of linen and wool banned in multiple places in the Torah.

Where does the notion of shatnez come up in primary texts? Leviticus 19:9 proclaims, “You shall not let your cattle mate with a different kind; you shall not sow your field with two kinds of seed; you shall not put on cloth from a mixture of shatnez.” Then the definition of shatnez is further unpacked in Deuteronomy 22:9-11: “You shall not sow your vineyard with a second kind of seed…You shall not plow with an ox and an ass together. You shall not wear shatnez — wool and linen together.” Wool of course, is an animal product. Linen is a type of cloth that is woven from threads that originate in the strong, fibrous flax plant — a crop with historic origins that has even been found in remnants in Ancient Egyptian tombs.

Like everything else in Judaism, there are plenty of interpretations when it comes to the meaning here. The 19th century German scholar, Rabbi Samson Raphael Hirsch wrote about the human compulsion to keep the balance between one’s conflicting animal, plant, and godly natures, with the wearing of shatnez throwing off this delicate chemistry. He explained, “We therefore believe we are not in error if we view the law against the intermingling of wool and flax in our clothing as a symbolic admonition not to permit our animal element to surrender to our vegetative stimuli, not to allow the former to be chained to, and interwoven with the latter.” For those who take the Torah literally, wearing shatnez-free clothing is understood as just one of 613 commandments and kept strictly, despite the fact that the reasoning behind the observance might seem puzzling, unclear, or even arbitrary. The term for such a statute in Hebrew is a chok.

It’s not prohibited to mix wool and linen in a single outfit (for example linen trousers and a wool cardigan), just in a single garment. Trying on items that might contain shatnez in a store dressing room or just out of the online shopping delivery box isn’t taboo either. Though testing guidelines are always changing as fashion manufacturing techniques become increasingly sophisticated, shatnez can be discovered in anything from winter boots and military uniforms, dresses and suit jackets, even tablecloths and carpets. Items like undergarments, bow ties, earmuffs, yarmulkes, wigs, and handbags are less likely to contain shatnez and don’t require testing. Interestingly, tzitzit are exempt and allowed to contain shatnez.

In the U.S., the shatnez-testing process typically takes place under a microscope operated by an authorized tester who has been trained and certified by the Association of Professional Shatnez Laboratories based in Lakewood, New Jersey. But in today’s age of heightened consumer awareness is this really necessary? Can’t the elaborate ritual of shatnez testing be entirely avoided simply by studying the well-marked, industry-mandated labels attached to the lapel of a sharp Zegna Hitchcock Grey Trofeo 600 suit? After all, that little silk rectangle states quite clearly that the gorgeous suit contains 85% wool and 15% silk.

Think again, cautions my local shatnez tester, Rabbi Zvi Solomon of the Boston Shatnez Laboratory.

“From the perspective of standards and consumer expectation necessary to properly observe the prohibition of shatnez, 99.9 percent of things are mislabeled,” he explains. It turns out that the labels only cover the exterior of a garment, but there are often other materials stitched inside. As an example, he pulls out a blue newsboy cap with a fancy “Made in Italy” label on its inner band. The label reads, 15% linen, 10% silk, 75% virgin wool. “So you would say this is 100% shatnez?” he asks. When the cap was tested underneath the microscope there was no wool, silk, or linen. The label is clearly a fake.

Rabbi Solomon runs the Boston Shatnez Laboratory out of his family home, a typical New England Colonial set smack in the middle of Orthodox Brighton. Customers call ahead, then leave the items they want to have tested on an enclosed porch along with handwritten notes. A clothing rack is filled with branded garment bags, the floor below littered with Crocs and muddy sneakers belonging to the Rabbi’s six children.

Rabbi Solomon’s busy seasons come right before the High Holidays and when all the college students, especially the Harvard kids, get their internships and need to have their suits checked over. Interestingly, Purim — the Jewish holiday in which even the most somber Jews let loose — is particularly manic, with a lot of rush jobs for checking over last minute costume purchases.

Offering me a takeaway cup of instant coffee from a giant thermos, Rabbi Solomon creaks open the door to his basement, and I follow him down the stairs to his laboratory. One wall is filled floor-to-ceiling with religious books. In the corner, his grey desk is packed with tools, including a microscope as well as a drawer brimming with seam rippers in various sizes. He hasn’t counted in a few years, but he estimates that around 150 people regularly drop off garments to be tested for shatnez, a process he conducts by fluorescent lamp light after 10:30 p.m. when his day job as Rabbinic Kosher Coordinator for KVH Kosher — a division of the Rabbinical Council of New England — is done and the kids are snug in bed.

He charges a nominal fee, considering his work a service rather than a business.

“A community has to provide its Jewish constituents the ability to observe the mitzvot, so a mohel, a sofer scribe, and so on,” he explains. “It’s necessary that the Jewish community as a whole have someone who can help people observe the mitzvah of not wearing wool and linen together.”

The term shatnez itself is an acronym for three verbs related to the production of clothing, shua, tuvi, and nuz. The Boston Shatnez Laboratory website states that, “Although there are differences as to exactly which processes are being referred to, most opinions maintain that shua refers to the combing of the raw fiber. Tuvi is the process of spinning fibers into a thread, and nuz refers to the twisting or weaving of the threads into cloth.”

Rabbi Solomon grew up observing shatnez but didn’t know much about the testing process until he was given the role by rabbis at Kollel, an Orthodox learning institution that serves the greater Boston area. He first spent a week in New Jersey gaining certification with The International Association of Professional Shatnez Laboratories, an organization that strives to standardize the shatnez testing process.

“The training entailed learning about the garment manufacturing, places in clothing where they would want to put linen, and also microscopy, to be able to identify fibers,” he says. One doesn’t need to be a rabbi to test for shatnez, and women can also be qualified as shatnez testers. “I sense that women make even better shatnez testers than men, mainly because they tend to be more familiar with different fabrics and garments.”

Before the advent of the American department store in the late 19th century, people of some affluence visited a private tailor to have their clothes custom-made. It was common to come with fabric in tow, and for those who observed, to first take that fabric to a local shatnez tester for verification. Synthetic fibers, or plastic threads, weren’t invented yet, and as a result it was once much simpler for a shatnez tester to eyeball fabric without a microscope and know what it contained. A last-ditch resort was always to burn a small sample of a fabric and observe the results, as wool and linen burn differently. In 1941, Joseph Rosenberger, an Austrian immigrant and Holocaust survivor, established Williamsburg Shatnes Laboratory, the first of its kind in the United States.

Today’s shopping industry is truly global — which means many more choices, but also complexities. The fabric for a jacket might be sourced in Italy, with the buttons coming from a factory in China. The shoulder area might be reinforced with synthetic materials made in Bangladesh. And the whole shebang can be bought online with one click and a credit card, rather than prepared from scratch by the trusted family tailor.


Pointing to a Ralph Lauren blazer hanging from the handle of a filing cabinet Rabbi Solomon says, “The label just told me the fabric. Inside the collar you probably have a felt lining.” It’s analogous to buying a house. “They aren’t telling you what’s behind the sheetrock. You know you have plumbing, but you don’t know how it works.” He gestures to my Weekend Max Mara denim jacket. “The label on your jacket surely reads 100% denim. But what are the buttons made of? Or that the stitching is synthetic nylon.” The consciousness to detail that shatnez testing requires is profound.

Adjusting his glasses and bending towards the lamp, he begins to test the Ralph Lauren blazer so I can experience the process firsthand. First, he daintily separates the collar stitching with a seam ripper, probing at the material inside.

He explains what he’s doing: “Typically, under the collar that surrounds the neck is the place that needs reinforcement. Here that’s with a felt. If you were making it a very good quality, you would put in linen canvas. Linen has a luster, a shine. Felt or cotton has more of a dull look. Synthetic fabric also has a shine.” Although when he first began, Rabbi Solomon needed to verify every finding with a microscope, over time he’s developed the ability to discern most fabrics with the eye alone.

He finds some shatnez inside the collar — which is made of wool felt twinged with linen threads. Rabbi Solomon removes the shatnez material. Next, he will send the customer to the tailor with a note and some new fabric for alterations. He says, “I cut the old material to deter him from wanting to put it back in.” Some shatnez testers are tailors themselves, but in the case of Rabbi Solomon, the Boston Shatnez Laboratories has built a relationship with a local non-Jewish tailor, Christos over on Harvard Street in nearby Brookline. “He completely removes the shatnez and seals up the seams,” says Rabbi Solomon. “Then the customer returns the garment to me to make a final verification.”

Pulling a little machine out of his desk drawer, the rabbi shows me his own bespoke non-shatnez labels which he affixes to any garment he’s tested for shatnez that either passed the exam with flying colors or was successfully altered. “Before I can affix the non-shatnez label, they bring it back to me and I verify that the new material was inserted,” he explains. He goes on to look inside the the shoulder pads and to assess the type of tailoring tape used at the cuffs of the sleeves.

The general understanding in the Orthodox community is that your body can’t be dressed in shatnez or derive warmth from an object that contains shatnez. So for example, a tablecloth might give your lap warmth. The same thing goes for a baseball glove, which might be lined in shatnez. Or even the coziness of sitting on the sofa on a chilly night. Rabbi Solomon doesn’t typically get invited to do house calls, though he did once get asked to check out a carpet at the local Modern Orthodox day school.

One winter, he got a number of worried enquiries about the possible presence of shatnez in UGG boots. Apparently in Australia, there was one model of UGG with a lining that contained both wool and linen. Boston Shatnez Laboratories maintains an updated list on its website of items that should be tested as well as those that most likely do not contain shatnez. There is also a lineup of name brands and labels that tend to have shatnez. It’s not meant to discourage support for those brands, but simply to act as an educational tool for consumers so they can budget in the potential costs of shatnez testing and alteration before making a purchase.

But are the brands themselves aware of shatnez concerns? Back in 2007, some ultra-Orthodox Israelis raised an uproar upon finding that several trendy men’s suits at Zara contained shatnez but were mislabeled. As the biggest retailer in the country, Zara quickly backtracked and apologized for the “production error,” and promised to more accurately label all garments in the future.

Back in Boston, Miltons, a classy menswear store which has been in business since 1947, has a special deal going with Rabbi Solomon reimbursing customers for all shatnez testing expenses. Owner Dana Katz says clients asking if a suit contains shatnez is “something that has been going on for years and of which many manufacturers are aware.” He’s seen certain labels become increasingly conscious of shatnez found within their garments in places beyond where the eye can see. These include Hugo Boss, Ted Baker, Jack Victor, and Bartorelli Napoli — which is produced in Asia but owned by an observant Sephardic Jew.

He explains, “Our vendors may switch factories of production. We just can’t say with certainty that a factory that Hugo Boss is using this season will have no problems in terms of shatnez. That’s where testing comes in.” As a result, Katz has educated all of his salespeople, most of whom are not Jewish, to be aware of shatnez and able to inform customers of how to get their purchases tested accordingly

Although compact, the Orthodox community makes up a loyal consumer bloc. “Certainly in today’s market, when you think about who wears tailored clothing, more religious [Jewish] people wear tailored clothing than those aren’t observant,” muses Katz.

I end my visit to the Boston Shatnez Laboratory squinting into the microscope at various fabric swatches. There’s a sort of wordless poetry to the way the textiles look close up — a reminder that wool actually comes from an animal’s curly coat; the tiny buds of linen shining through the glass slide are still traceable to the field where they originally grew from tilled dirt. Whether or not one believes in the concept of kosher clothing, the idea of shatnez forces a kind of elevated consciousness into the origins, production, and accessibility of today’s fashion. Strumming the brass buttons on my denim jacket on the walk home, I feel a newfound sense of appreciation for my closet full of clothing that I didn’t have to grow, shear, card, spin, or sew with my own clumsy hands.

Danna Lorch is an American arts & culture writer based in Boston. She recently relocated back to the US after seven years spent covering the emerging art, fashion, and design scene in Dubai. Recent work has appeared in Vogue Arabia, Architectural Digest Middle East, L’Officiel USA, ARTnews and elsewhere. She holds a graduate degree in Middle Eastern Studies from Harvard and is interested in the intersection of art, fashion, and faith. Find her on Instagram and Twitter

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