The effect of furnace atmosphere on E-glass foaming has been studied with the specific goal of understanding the impact of increased water content on foaming in oxy-fired furnaces. E-glass foams were generated in a fused-quartz crucible located in a quartz window furnace equipped with video recording. The present study showed that humidity in the furnace atmosphere destabilizes foam, while other gases have little effect on foam stability. These findings do not contradict the generally accepted "dilution model", suggesting that foaming is more severe in oxy-fired furnaces than in air-fired furnaces because the higher concentration of water in the furnace atmosphere ultimately enhances sulfate decomposition resulting in stronger foaming. The failure to reproduce this effect in Corresponding author.