In open molding, raw materials (resins and fiber reinforcements) are exposed to air as they cure or harden. The product shape is determined by a single-sided mold that serves as a free form surface. So, all materials are assembled only ON that surface.
Open molding is the most flexible of all composite fabrication processes as part size and design options are virtually limitless. Typically, the open molding process is used for a large size range of products that cannot be produced in more automated processes, or for parts that are produced in low volumes that cannot justify the higher mold costs of automated processes.
Tooling cost for open molds is often inexpensive, making it possible to use this technique for prototype and short production runs.
It is a low-cost, common process for making fiberglass composite products. It is typically used for boat hulls and decks, RV components, truck cabs and fenders, spas, bathtubs, shower stalls and other relatively large, noncomplex shapes.