[TJSomething]

Another part from the paper that a lot of people here seem to be ignoring: "Specifically, macroscopic water droplets isothermally form when the NP size is ≤22 nm, RH is >~90%, and ϕPE ranges from 0.05 to 0.35." and "Initial water droplets that are observable under optical microscopy (~1 μm in size) appear within a few seconds after being exposed to 97% RH."

This is really moist air that's only barely short of forming dew. A lot of people are focusing on sensational "violation of physics", when it's an incremental improvement on process that happens naturally.

[TimByte]

I think the interesting bit is less about "breaking physics" and more about how finely tuned the material is to encourage this behavior without external cooling.

[vel0city]

But there was external cooling, or am I reading "The temperature of the films was controlled" incorrectly?

[bm62]

He likely means cooling it below the dew point rather than controlling the temperature in general.