Quasi-isotropic laminate

The specified order and orientation of the plies through the thickness of a laminate, usually written as a shorthand code of ply angles. It governs the laminate's stiffness, strength and coupling behaviour, and is fixed on the drawing as part of the laminate schedule.

A laminate whose ply orientations and materials mirror each other about the mid-plane. Symmetry prevents coupling between in-plane loads and bending, so the laminate remains flat after cure instead of warping.

A laminate that contains, for every angled ply, a matching ply at the equal and opposite angle, eliminating coupling between in-plane extension and shear. Balanced, symmetric laminates are the default choice where predictable, distortion-free behaviour is required.

Reinforcement in which virtually all fibres run in a single direction, supplied as dry tape, lightly stitched or bound fabric, or prepreg. Unidirectional plies give the highest stiffness and strength along the fibre direction but need supporting plies in other orientations.