A sensor (10) for detecting directional variations in a physical characteristic, fiber orientation angle and the degree of anisotropism of a moving sheet of material is disclosed. The sensor (10) has a support (12) for supporting the moving sheet (14). The support (12) defines an open region into which the moving sheet (14) is deflected by a deflector (16). Detectors (20) coupled to the support (12) detect and produce signals indicative of the force exerted on the support (12) by the deflected sheet in at least three different directions. Alternatively, the support (112) may be rotatable to allow detectors (120) coupled to the support (112) to detect and produce signals indicative of the force exerted on the support (112) by the deflected sheet (114) in a number of different directions. Each signal is processed to determine a physical characteristic, such as extensional stiffness, of the sheet of material in each of the at least three directions.