Corning polypropylene Erlenmeyer flask caps are also available separately. These caps fit both Polycarbonate (PC) and Polyethylene terephthalate glycol-modified (PETG) Erlenmeyer Flasks and are available for the 500 mL and 1L, 2L, 3L, and 5L flask sizes. Corning polypropylene Erlenmeyer flask caps are also available separately. These caps fit both Polycarbonate (PC) and Polyethylene terephthalate glycol-modified (PETG) Erlenmeyer Flasks and are available for the 500 mL and 1L, 2L, 3L, and 5L flask sizes.