The much-anticipated Ultrafly arrived with a big surprise, featuring Vaporweave—a technology that seemed to have been abandoned by Nike after its debut in the first-generation Vaporfly.

Vaporweave is an ultra-thin mesh that faced criticism for poor breathability. So, our expectations weren't high before testing, particularly because the Ultrafly combines this mesh with a comfort-focused fabric underneath as can be seen in the video above.

However, the Ultrafly earned a 3/5 in our smoke-pumping test, which is not a bad result for this type of plasticky upper.

Using a light, we confirmed that the Vaporweave upper doesn't have any big breathability holes, a common feature in trail running shoes.

Under the microscope, we discovered some tiny holes responsible for the shoe's average breathability score. Without these holes, the shoe would have likely scored a 1/5.