The composition, shape, and size of fiberglass products vary significantly from one facility to the next, and even from one production line to the next. However, the mold fabrication process for rigid fiberglass and fiberglass reinforced plastic (FRP) products is similar for most different shapes and sizes.

Open-molding or "hulled" fabrication typically uses these process steps:

• Prepare mold, including mold release agents
• Apply gel coat and allow to cure
• Add fiber and resin, initiators, catalyst, and adhesives or inert fillers (as applicable)

  - For spraying applications, chopped fibers, resin and catalyst can be applied at the same time with separate applicators, or mixed and sprayed from a "chopper gun"
  - For hand lay up of fiberglass laminate or mats, the mats are placed first, then sprayed with the resin and additives

• Roll layers to remove air bubbles and create uniform density and thickness
• Repeat spray (and laminating if applicable) until all layers are added
• Cure at varying time and temperature, depending on the workpiece size and shape, throughput rates, and resin cure requirements
            Most poly-based resins cure at ambient temperature,
            while epoxy-based resins cure at elevated temperatures
            that usually require an autoclave or oven.
• Demold
• Clean mold, tooling, rollers, transfer hoses, drums, spray guns, and other tools and equipment that come in contact with resins
• Trim the molded piece
• Complete finishing operations (e.g., adding foam for insulation, lightweighting, or structural support, upholstering, coating, painting, padding and carpeting)

Closed molding uses a two-part mold and is suitable for almost any shape that is conventionally "hulled" or open-molded. This process includes vacuum molding, infusion molding, resin transfer molding (RTM), and/or Seemann Composite Resin Infusion Molding Process (SCRIMP). Due to the closed, sealed mold during polymerization, it generates significantly less emissions than open molding. Typical process steps:

• Prepare mold, including mold release agents
• Apply gel coat and allow to cure
• Spray fibers onto gel coat layer, or manually place reinforcing media in mold (typically continuous strand glass fiber mats)
• Close the mold and draw a vacuum to seal contact areas
• Inject catalyzed resin (and other additives) to coat the perimeter then apply vacuum near part center to draw resin through entire part
• Cure at varying time and temperature, depending on the workpiece size and shape, throughput rates, and resin cure requirements
            Most poly-based resins cure at ambient temperature,
            while epoxy-based resins cure at elevated temperatures
            that usually require an autoclave or oven.
• Demold
• Clean mold, tooling, rollers, transfer hoses, drums, spray guns, and other tools and equipment that come in contact with resins
• Trim the molded piece
• Complete finishing operations (e.g., adding foam for insulation or structural support, upholstering, coating, painting, padding and carpeting)

Centrifugal molding involves a spinning mold and is used in manufacturing cylindrical products such as tanks or pipes. Centrifugal molding also generates significantly less emissions during polymerization than the open molding process. The typical unit processes are:

• (For tank production, install a base piece before starting sidewall production)
• Spray side walls of the spinning mold with a layer of resin or gel coat
• Spray the resin and catalyst (and adhesive if applicable) saturated with chopped strand glass into the mold
• Allow to spin to remove trapped air bubbles and ensure a dense uniform laminate
• Repeat application of resin and fiber layers to meet the design wall thickness
• Cure and demold
• Clean mold, tooling, rollers, transfer hoses, drums, spray guns, and other tools and equipment that come in contact with resins
• Trim the molded piece

Additional supporting operations and important facets of fiberglass manufacturing which require environmental management are air filtration and ventilation, chemical management and storage, finish operations (e.g., adding foam for insulation or lightweighting or structural support, upholstering, coating, painting, padding, carpeting and accessorizing), solid waste management, recycling and reuse, and energy and water use.

Typical inputs to fiberglass fabrication can include (but are not limited to):

• Cleaning cloths or rags for equipment and mold cleaning
• Mold release agents, typically wax- or polymer-based
• Gel coatings
• Solvated resins which surround and hold fibers to create the composite material
• Initiators and catalysts
• Fibers or fiber sheets or mats or roving
• Styrene a solvent and co-reactant in the polymerization process
• Vapor suppressants
• Emulsifiers
• Inert fillers
• Foaming agents (typically polyester-based, although isocyanate-based foams which are more toxic are still used)
• Solvents (may contain acetone, toluene, xylene, various alcohols, other chlorinated compounds, or citrus extracts)
• Paints and thinners
• Adhesives

Typical outputs of fiberglass fabrication can include the following, many of which are hazardous depending on the nature of the raw material:

• Solvent or resin-laden cleaning cloths or rags
• Spent or residual mold release agents
• Solvated or residual resin, including gels that have cured before they could be used
• Scrap and waste reinforcement fibers, mat, cured trim ends and cut-outs, foam, other
• Air emissions
            - Styrene (from resins and gel coats)
            - Toluene (from some mold release agents)
            - Dimethyl phthalate (from some catalysts)
            - Other volatile organic compounds (VOCs)
              and hazardous air pollutants from solvents,
              catalysts, resins, foams, paints, and other raw materials
• Surplus, waste and/or expired chemicals: solvents, initiators, catalysts, resins, paints, stains, foams, adhesives, etc.
• Overspray solids
• Spent solvents and still bottoms
• Spent filters

A number of alternative processes and materials can minimize environmental impact and worker exposure during fiberglass manufacturing. See Pollution Prevention Opportunities for a list.