"The garment's fabric must be made of woven material. A plastic poncho-style raincoat or a four cornered leather vest would not require tzitzis because the material is not woven. Also, it is the opinion of a leading Torah authority that garments woven with synthetic fibers do not require tzitzis. This means that a polyesteror rayon garment does not require tzitzis. What about a wool-rayon blend, which is a blend of natural and synthetic fibers? The criteria for determining tzitzis obligation is which of the two fabrics coversthe majority of fabric area. If, for example, the fabric is a 50-50 blend of natural and synthetic fibers, but the synthetic thread is thicker than the natural, then the garment would not require tzitzis.Wearing an Arba Kanfos (beged with tzitzis) made of synthetic fabric would present the problems stated earlier: 1) non-fulfillment of the mitzvah, 2) uttering a blessing in vain, 3) carrying on Shabbos."http://www.star-k.org/kashrus/
Material Requirements: Halachipedia
"Sephardim generally follow the opinion of the Shulchan Aruch that only garments made of wool or linen have a torah obligation to be affixed with tzitzit strands. Accordingly, all other materials only require tzitzit on a rabbinic level. As such, it is preferable for one to wear a wool or linen garment. Nevertheless, it one finds ituncomfortable to wear wool tzitzit, he may wear tzitzit made from other materials. Ashkenazim rely on the Rema who holds that all materials are included in the Torah obligation. Nevertheless, some maintain that one still should wear wool and linen garments in order to satisfy all opinions.  One the other hand, many poskim are lenient if wearing wool would cause any discomfort, especially in the heat. Although the Shulchan Aruch includes linen as a biblically mandated material, he also cites 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 abracha. Leather garments are exempt from the obligation of tzitzit, even on a rabbinic level.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. 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. For a discussion of using Techelet (blue) strings as Tzitzit see the Techelet page.The minhag for sehpardim is that the garment and tzitzit be of the same color. "http://halachipedia.com/index.