Unidirectional fabricUD

A family of reinforcements in which straight, uncrimped layers of fibre are held together by stitching or bonding rather than by weaving. Avoiding crimp improves stiffness, strength and fatigue performance compared with equivalent woven fabrics, and the format suits automated handling and the infusion of large parts.

Reinforcement fibre pre-impregnated with a controlled quantity of resin, usually a partially cured (B-staged) thermoset, supplied in rolls and stored chilled or frozen until layup. Prepregs give precise fibre and resin content and are the standard material form for high-performance aerospace and motorsport laminates.

A bundle of thousands of continuous carbon filaments handled as a single unit, the carbon fibre equivalent of a glass roving. Tows are designated by their filament count in thousands, written with a K, and are used directly in filament winding, automated fibre placement and weaving.

The proportion of a composite's volume occupied by fibre, a key measure of laminate quality and the main driver of stiffness and strength in the fibre direction. It is determined by methods such as resin burn-off, acid digestion or image analysis of polished sections.