Layup is the planned arrangement of layers in a composite part before it is formed or cured. Each layer, or ply, may use a different fiber direction, thickness, or material, and the stack is built to achieve a specific balance of strength, stiffness, weight, and flexibility.
Layup matters because composite performance depends heavily on layer order and orientation. A poor layup can create weak spots, trapped air, delamination, or warping, while a well-controlled layup produces a lighter, stronger, and more reliable part. In manufacturing, technicians follow a layup schedule and inspect the stack before curing, since defects are much harder to fix after the resin hardens. In the RV countertop example, the layup helps determine whether the finished surface is merely light or also durable enough for real use.