An inflection layer is the region of space between the two layers of a cube. It can be regarded as the polar opposite of a commissure.
Unlike in a commissure, from the vantage point of an inflection layer, the strange geometry of the Manifold Sky is visibly apparent. As an observer gets close to an inflection layer, the layer of the cube they are ascending from (their origin layer) appears to "unfold," becoming distorted until, at the inflection layer, the origin cube layer far below appears to be a vast, flat plane that extends all the way out to a horizon, with terrain features endlessly repeating. At the same time, the cube layer far above (previously appearing as a distant point or "sun" in the center of the cube) appears to unfold as well, gradually becoming a vast, flat plane that extends all the way out to the horizon in the same manner (albeit effacing) as the layer the observer just left has unfolded.
The air pressure within an inflection layer is extremely low, since the inflection layer is effectively the highest boundary, in terms of altitude, that objects within a cube can reach. Non-buoyant objects in an inflection layer will eventually drift toward one of the layers and then accelerate towards it; while the gravity of the layers does cancel out in the absolute middlemost region of the inflection layer, eventually the gravity of whichever layer is closer to the object will overcome that of the (now receding) more distant layer. Conversely, objects sufficiently buoyant to reach this altitude (such as dirigibles), will be pushed towards the middlemost region of the inflection layer, being forced to either exert thrust or somehow reduce buoyancy to descend towards one cube layer or the other. It is this feature of inflection layers that enables skystations to maintain their altitudes passively.