- We quantify the impact of work in process (WIP) bubbles on a semiconductor fab. As a preliminary step, we formalize the concept of WIP bubbles by decomposing them into local events of relatively acute and temporary WIP congestion. The local bubble is empirically identified and its impact on local waiting time distribution is assessed. We then estimate its marginal impact on the overall line waiting time and cost. Finally, a novel visualization tool for the bubble's progression is proposed.