Layup

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.

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.

Intermediate vacuum compaction of a partially completed prepreg stack, carried out periodically during lay-up to remove trapped air and seat the plies before further layers are added. Regular debulks reduce wrinkling, bridging and final void content, especially on curved tooling.

A consolidation technique in which a laminate is sealed under a flexible airtight film and the air is evacuated so that atmospheric pressure compacts the plies during cure. It removes trapped air and excess resin and is used with wet lay-up, prepreg and infusion processes.

The degree to which liquid resin has penetrated and coated the filaments of a reinforcement, visible in glass fabrics as a change from opaque white to translucent. Complete wet-out is essential to laminate strength, since dry patches act as built-in defects.