May one clean his glasses with the Tallit he wears during prayer? The Mishna Berura (21:12) cites two views as to whether one may use a Tallit that still has Tzitzit strings for a purpose other than the Mitzva. (Of course, all views would forbid using the garment for a denigrating purpose, such as cleaning one’s body.) He then cites the Peri Megadim as clarifying that according to all views, the Tallit designated for use during Tefila may not be used for any other purpose; therefore, one may not clean his glasses with the Tallit worn during the prayer service.
May one clean his glasses with his Tallit Katan?
Yes; the Mishna Berura (21:12) writes that one may use his Tallit Katan for any purpose that is not denigrating.
SOURCE: http://www.mishnaberura.com thanks to apushatayid for leading to this resource