Unidirectional fabrics achieve high structural properties because their fibers are:

Unidirectional fabrics are designed with fibers that are straight and uncrimped, which means that they run parallel to each other without any bends or twists. This arrangement allows the fibers to carry loads more effectively along the direction of the fibers, providing maximum strength and stiffness in a specific orientation. The aligned fibers contribute to the overall structural performance by ensuring that the material can efficiently transfer applied forces, leading to improved mechanical properties such as tensile strength, flexural strength, and durability.

In contrast, fibers that are crumpled or curved do not contribute to mechanical performance in the same efficient manner, as their orientation would lead to energy dissipation and reduced load-bearing capabilities. Additionally, fabrics with randomly oriented fibers do not provide the targeted strength that unidirectional fabrics offer, thus they are less effective in applications requiring high structural integrity along specific axes.