Sep 27, 2021 · Voa Vials Caps at Thomas Scientific. VOA VIALS are most often used for volatile organic compound analysis. Available in clear 33 expansion and amber 5 expansion borosilicate glass. Open top vials come assembled with polypropylene caps with low-bleed 0.25" PTFE/silicone septa inserted (.35" septa for E-series vials). Sizes.