http://revach.net/article.php?id=373

Section: Halacha   Category: Tshuvos
Tzitzis - Why Did the Chazon Ish Wear a Cotton Beged?

The Shulchan Aruch (OC 9:1) paskens that only wool or linen garments are Chayav in Tzitzis Min HaTorah.  Other materials such as cotton are only Chayav M'DiRabanan.  Although the Rema argues, the Mishna Brura says that a Yarei Shamayim should wear wool to be on the safe side. The Vilna Gaon wore cotton and the Chazon Ish relied on him to do the same. Why?

Some say since they wore linen shirts the Gra was machmir that a linen shirt over wool tzitzis may be shatnez. Rav Chaim Kanievsky is quoted as saying that the Chazon Ish told him the Gra wanted people to know that cotton is okay for tzitzis because if they thought only wool was permitted, they would not wear tzitzis in the summer at all since it is too hot. Others say because wool gets dirty and is difficult to wash it is better to wear cotton. (Piskei Tshuvos)

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.