27.25 x 57.5 mm, 5 dram (20 ml) Clear borosilicate glass vial with 24-400 black phenolic polycone lined cap attached. clear vials offer maximum visibility. made of type i borosilicate glass, providing exceptional resistance to heat shock and chemical leaching. The glass is non-porous and has no catalytic affect. Because the boron oxide particles in the glass are so small, the silicate is held more closely together, resulting in a much stronger glass for your laboratory needs. Attached black phenolic caps with polyseal cone liners form an exceptionally tight seal and offer a good chemical barrier. This liner molds itself around the sealing areas of the finish as the cap is screwed on, virtually eliminating leakage, evaporation, contamination, binding and backing off.