Borosil® Flat Bottom (Florence) Boiling Flasks have uniform wall thickness for even heat distribution. Constructed from stress-free borosilicate. Borosil® Boiling Flasks are heat-resistant. Built to withstand the demands of the modern lab, each flask has a flame-polished, beaded rim for added strength, & an enamel area for marking. Available from 25mL to 20L. Flasks comply with ISO 1773. 25mL, 150mL, 300mL, 3L, 5L, & 20L options not covered in ISO. In collaboration with Borosil Glass Works, Foxx Life Sciences is proud to bring the outstanding quality of Borosil® Type 3.3 Borosilicate glassware to North America for the first time. Manufactured from the same USP Type 1 borosilicate glass that North American scientists have come to trust, Borosil® Laboratory Glassware offers unparalleled mechanical strength, clarity, & reliability at competitive prices. & thanks to a unique annealing process, Borosil® Glassware is stress-free & incredibly resistant to thermal shock.