An anisotropic material's material properties vary with direction within the material. A well made road bike demonstrates this phenomena. The side to side stiffness of a bike is very high so that maximum power is transfer from the pedals and crank arms to the rear wheel. However the same stiffness in the vertical direction, think of a line moving from the real axle to the seat post, would be undesirable. if this segment of the bike frame where stiff, all the bumps in the road would be transferred to the butt and back of the rider. This portion of the bike frame is much more flexible than the rest of the bike.
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