An experimental setup was constructed to record the real-time mass data of eight pure polymers under the UL94 vertical burning test conditions. The experiments showed that the flame rises up to the clamp or the dripping occurs soon for the pure polymers. The mass burned before the flame reaching the clamp and the dripping occurrence only accounts for a small fraction of the original mass of the specimen, which differentiates the UL94 test from the cone calorimeter test. The mass loss rate of polymer specimens is in the magnitude order of 0.001–0.01 g/s. It was also found that the flame of thin specimens usually reaches the clamp sooner than that of thick specimens. Apart from the dripping behaviors found in large-scale fires, it is found that the diameter of the first drop for the tested polymers is in the range of 2.0–10.0 mm. The mass of the first drop increases with the first dripping time. The first dripping time and the mass of the first drop increase with the thickness of the specimen, especially for polymers of large-size dripping type. Copyright © 2009 John Wiley & Sons, Ltd.