According to some, Jewish people get buried in a Kittel. Is there a difference in the Halacha if the Kittel is pure linen or not?
Shulchan Aruch (Yoreh De'ah 301:7 and 351:1) states that tachrichim (burial shrouds) may be made from shaatnez. Which would mean that, from the point of view of halachah, they don't have to be pure linen.
That said, Pischei Teshuvah (351:2) cites Yalkut Reuveni that for kabbalistic reasons only linen should be used, and not a single stitch should be of any other material.