The in-plane permeability was measured for thick, unidirectional oriented strand lumber made from aspen (Populus tremuloides) strands and pressed to five different densities. The press cycle was such that the vertical density profile of the panels was uniform. Specimens were cut from the boards and sealed inside a specially designed specimen holder; this jig was connected to a permeability measurement apparatus and in-plane permeability measured parallel, perpendicular, and 45° to the strand orientation. Permeability decreased markedly with increasing board density. The highest permeability was in the strand alignment direction and lowest perpendicular to it. The permeability in the 45° direction fell between those in parallel and perpendicular to strand alignment. A polynomial equation was fit to the results of each direction with r2 of 0.938 and 0.993. The in-plane distribution of permeability as a function of flow direction was obtained and its vector diagram was lenticular in shape.