Question: I have just moved into a new home and need to kasher the kitchen. What is the halacha regarding the formica countertops? Is it the same for plastic utensils?
Answer: There is a machlokes among the rishonim as to how to treat materials that aren’t mentioned in the Torah.
Thus, for example, while most rishonim including the Shulchan Aruch (OC 451:26) hold that as glass is non-absorbent, it does not need to be kashered, the Rema follows the Mordechai (Pesachim 374) who writes that glasses can’t be kashered for Pesach because they are made from sand and therefore similar to earthenware.
R’ Yechiel Yaakov Weinberg (Seridei Aish 1:46) writes that the acharonim are lenient regarding plastic and such utensils may be kashered through hagalah (placing in boiling water). R’ Eliezer Waldenberg (Tzitz Eliezer 4:6:3) compares plastic utensils to stone ones and permits kashering through hagalah.
R’ Yitzchak Yaakov Weiss (Minchas Yitzchak 1:86; 3:67) writes that while one shouldn’t specifically buy non-kosher plastic utensils, if one’s plastic utensils became treif, one may kasher them. One should avoid doing this to kasher for Pesach.
R’ Moshe Feinstein (Igros Moshe OC 2:92) wrote that while one may kasher natural rubber, one cannot kasher materials made from synthetic substances (See Igros Moshe EH 4:7 regarding Teflon). R’ Shimon Eider (Halachos of Pesach 13:n5; 10) writes that R’ Moshe told him that this only applied to kashering for Pesach. One may use hagalah to kasher during the year, however.In conclusion, while most poskim don’t allow one to kasher plastic or formica countertops for Pesach, one may do so during the year when necessary.