Question:
I heard that many Chassidic Jews prefer to wear woolen tzitzit, as opposed to cotton, which is much more comfortable. Why?
Response:
In the Talmud, there is an opinion that one is Biblically obligated to affix tzitzit, the ritual fringes that are on the corners of the prayer shawl, onto a wool or linen garment only.
This is learned from a verse where it states in regards to a specific law involving clothing,1 “a woolen garment, or on a linen garment.”2 From here some learn that when it says “garment” in the Bible in the context of a commandment, it is referring specifically to wool and linen garments. Therefore, the commandment to place fringes on a four-cornered garment—“You shall make yourself twisted threads, on the four corners of your garment with which you cover yourself”—is referring specifically to a wool or linen garment.3
According to this tradition, placing fringes on garments made of other materials, such as silk, is a rabbinical requirement, not a Biblical one.4
In his gloss on the Code of Jewish Law, Rabbi Moshe Isserles, known as the Rema, rules that garments of all fabrics are equally Biblically required to have fringes.5
Nonetheless, it is preferable to wear a prayer shawl that is made of wool,6 since it is Biblically required according to all opinions.7
But, you ask, if there are reliable rabbinic authorities who rule that cotton is okay, why sweat with wool? I guess the key here is that mitzvahs are more than just paying dues to the Great Supernal I.R.S. We do them because we love Him. Sure your spouse can subside on tuna and crackers, but serving them their favorite dishes transforms it into an act of love. And wearing the kind of garment that we are sure warrants a mitzvah does the same thing.

It is quite curious to me that cotton is not mentioned in Chumash. Or is it?
Egypt is well-known for its high-quality cotton fabric, so I imagine cotton was a fabric available in Torah times. Yet we read about linen and wool only. And there are different quality levels of both linen and wool ... The Eshet Chayil (Woman of Valor, from Mishlei) wears garments of purple linen. The poem also states that her household does not fear cold weather, for they are clothed in scarlet wool ... yet a tzniutdik woman is not permitted to wear a red garment ... Information with sources cited are welcome, PLEASE!
"She seeks wool & flax" - is she looking for shatnez?
Cotton was not cultivated in that area of the world until the Middle Ages. Egypt only began cotton production within the last 2,000 years. Cotton was so unknown outside of the Far East that Europeans thought it grew on a hybrid lamb-plant that was attached to the ground called the Vegetable Lamb of Tartary.
The Or Chadash (p. 1030) writes that when it says that her family wears scarlet, it must have been referring to indoors, not in public. Or, it refers to strips of scarlet, not entire garments made of scarlet. See the Aruch to Brachos 20a.
Thank you very much, R. Adelman, for this reply! With sources!
I have been very curious, but have not found satisfactory answers on the internet.
Per the Wikipedia history of cotton page, cotton was grown and woven into fabric in NE Africa around 5,000 BCE. (The page refers to the kingdom of Kush, which is mentioned in Chumash.)
Like cotton, linen is made from a plant (flax). Flax requires a lot of human effort to transform and process it into linen, yet it's in Torah.
I still wonder why it took humans so long to "figure out" cotton? Cotton is always my fabric of preference ... it's cool in warm weather, warm in cold weather, easily woven or knit, washable, and takes dye well. And HaShem neither proscribes nor limits its use!
May HaShem Yirachem reveal Mashiach to us soon, and may he answer our questions both prosaic and spiritual, and help us more fully to understand the connections between gashmiut and ruchniut!
.
where do you find cotton tzinius dresses?
I recently saw a source (sorry, I can't remember where) that said that Jews do not wear red clothing because the color, which is pronounced "adom" in Hebrew, is another name for Esav ben Yitzchak. Esav was "supposed" to be the third of FOUR avot; he was the "beshert" of his cousin Leah. But he disrespected and discarded his Judaism, chas v'chalila. That's why there are three avot and four imachot ... Yaakov Avinu took both Leah and her sister Rachel (who was his true beloved) as wives so that Leah would fulfill her destiny, even without Esav/Edom as her husband.
I have found them in various places, including Target and Amazon. Kosher Casual, which is located in Israel and has a web store, is a good source for cotton clothing, too. I have some cotton dresses from April Cornell, and I've recently purchased some beautiful block-printed cotton dresses directly from India, via Etsy.com. If you keep your eyes open, you'll find cotton dresses at regular stores, occasionally (Anthropologie, Madewell). I enjoy fashion, so it's a hobby of mine to keep on the look-out, especially before chaggim, when I want to treat myself to something new.