Can I Make Pyrex Kosher?


I received a Pyrex dish that was most likely used for non kosher food. Is it possible to kosher this baking dish? If rekoshering is possible, is the process same as regular glass?



  1. A brief preface: Kashering “glass” is complicated because it is hard to define it according to Halacha. According to one opinion, glass does not have to be kashered at all because its surface is so smooth that it cannot absorb any flavor. Another opinion maintains exactly the opposite: glass cannot be kashered at all because it is made of sand and is Halachically considered earthenware. There is even another opinion maintaining that glass has the Halachic status of metal and can be kashered like metal.

    According to Rav Moshe Feinstein, Pyrex, Duralex and Corningware cannot be kashered – due to the concern that it might be made of sand and therefore “unkasherable.” There is a minority opinion that does allow for the kashering of Pyrex and other heat-resistant glass utensils by the process of Hagalah, meaning immersion in boiling water (see Shaarim Metzuyanim Behalacha Chapter 116:11 and Rav Ovadia Yosef, Yechave Daat, Volume 1, Chapter 7).

    Best wishes from the Team