ACP differentiates between four material classes: Materials, Fabrics, Stackups and Sublaminates.
The Materials class is the material database in ACP.
The Fabric class is where Materials can be associated with a ply of a set thicknesses.
The Stackup class is used to combine fabrics into a non-crimp fabric, such as a [0 45 90] combination.
The Sublaminate class is used to group fabrics and stackups together for frequently used lay-ups.
A Stackup or a Sublaminate can only be defined if a fabric and material have been defined previously.