Flow focusing geometry generates droplets through a plug and squeeze mechanism.

Microdroplets are typically generated by one of two microfluidic geometries, the T-junction and flow focusing. These two geometries are often thought to form drops through different mechanisms. Here, by directly measuring the pressures in the drop maker, we show that flow focus devices exhibit pressure fluctuations that are essentially identical to those found in T-junctions, suggesting that, in these devices and low-to-moderate capillary number, the drop formation process is also dominated by interfacial stresses and proceeds through a plugging-squeezing process.