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A wool tallit katan is considered the ideal, although cotton is also permitted according to halacha. Both the Chazon Ish and the Vilna Gaon purportedly used a tzitzit garment made of cotton.

Many refer to a wool tallit katan garment simply as “tzitzit,” or more aptly a tallit katan (or talit katan), which can be translated as “a small wrap-around garment.” Alternatively it is sometimes called “arba kanfos,” (or arba kanfot) which means “four corners.”

Some tzitzit wearers will "work up a sweat" merely hearing the word “wool,” but consider the following attributes:

• Wool garments resist grease and oils, which means they stay cleaner.
• Wool serves as a good insulator in the winter.
• Wool wicks moisture away from the skin, which keeps the wearer dryer while sweating and cooler in the heat.
• Wool is flexible and durable. It can bend 20,000 times without tearing, whereas cotton will break after 3,000 times.

The Shulchan Aruch states that a wool tallit katan garment is required to have tzitzit according to Torah law, while for other fabrics the requirement to tie on tzitzit is based only on Rabbinical decree. Most Sephardim follow this opinion, which the Mishnah Brurah recommends for Ashkenazim as well.