Pyrex (n.) Look up Pyrex at Dictionary.com
1915, proprietary name (Corning Glass Works, Corning, N.Y.), arbitrary coinage, in which eager etymologists see implications of Greek pyr "fire" and perhaps Latin rex "king;" but the prosaic inventors say it was based on pie (n.1), because pie dishes were among the first products made from it. The -r- is purely euphonious.