In forced wetting, a rapidly moving surface drags with it a thin layer of trailing fluid as it is plunged into a second fluid bath. Using high-speed interferometry, we find characteristic structure in the thickness of this layer with multiple thin flat triangular structures separated by much thicker regions. These features, depending on liquid viscosity and penetration velocity, are robust and occur in both wetting and de-wetting geometries. Their presence clearly shows the importance of motion in the transverse direction. We present a model using the assumption that the velocity profile is robust to thickness fluctuations that gives a good estimate of the thin gap thickness.We measured the dependence of the gap dimensions on the liquid viscosity, substrate width, and penetration arXiv:1807.11910v2 [cond-mat.soft]

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