#Although the Shulchan Aruch includes linen as a biblically mandated material, he also cites<ref>9:6; Also Kaf HaChaim 9:16. This opinion stems from Rabbenu Tam in Gemara Shabbat 25b</ref> an opinion that we should not use it. He concludes that although the halacha is not like this opinion, it is preferable to avoid the argument and only use wool. However, if one only has a linen garment for his tzitzit, they may be used with a bracha.<ref>Rema and Mishna Berura ad loc. This opinion comes from Teshuvot HaRosh 2:8</ref>
#Leather garments are exempt from the obligation of tzitzit, even on a rabbinic level.<ref>Gemara Menachot 40b. Shulchan Aruch 10:4</ref>
#Along the same lines, some poskim equate leather with synthetic materials (such as polyester, nylon, and rayon) and maintain that they are also exempt from tzitzit.<ref>Rav Moshe Feinstein in Igres Moshe 2:1</ref> Others differentiate between woven synthetic materials, which should be treated like cotton, and non woven synthetic materials, which should be treated like leather . Therefore, it is best not to use synthetic materials for the mitzvah, but if one does he should refrain from making a bracha on it .
== Making Tzitzit==