U

Unidirectional, or a UD, we refer to fibre optics (bundles and wires) as being oriented in only 1 direction. This way you can more easily determine the direction of your fibre reinforcement of your laminate. If you place 2 UDs on top of each other you obtain a bi-directional fabric. If you place 3 on top of each other, you obtain a tri or a so-called multi-axial fabric.