Molds can be built for one-time use to create a single part or they can be built to last decades and be used for production runs of thousands of composite parts. Regardless of the size, shape, or number of uses of the mold, the mold must meet several requirements:

1. The mold must be designed to be compatible with the manufacturing process used to create the part.

2. The mold materials must be compatible with the fiber-reinforcement and matrix material and must not adversely impact the final mechanical properties of the part. The mold materials must also be compatible with any mold release chemicals applied to the surface of the mold.

3. The mold must be designed to allow the cured composite part to be removed from the mold without damaging the part.

4. The mold must maintain sufficient dimensional stability throughout the manufacturing process to meet the dimensional requirements of the part.

Failing to meet any of these requirements will likely result in a composite part that is either dimensionally inaccurate, non-functional, cosmetically flawed, or a combination of all three. Beyond these basic requirements, there are not many restrictions governing what materials or methods must be used when constructing a mold. Molds can therefore be as simple as a flat metal plate used to create a sheet of carbon fiber or as complex as a CNC machined block of high density tooling board used to mold an aircraft fuselage. If only a single part is required, and its dimensional accuracy is less of a concern, the mold can be constructed with cost effective materials such as foam or wood and shaped with simple power tools or even carved by hand. If many parts are required and dimensional accuracy is critical, the mold will likely require more robust materials like aluminum or steel and must be manufactured with more precise equipment like a CNC router or a CNC mill.

The dimensional accuracy, quality, and surface finish of a composite part is directly related to the design and construction of the mold that is used to manufacture the part. Therefore, the materials and process used to create the mold will be driven by the requirements of the composite part. The number of parts, fiber type, resin type, fiber-to-resin ratio, surface finish, and temperature capability are some of the main requirements of a part that should be established before designing and manufacturing its corresponding mold.