Open Mold

Open molding is the most commonly used molding process in the fiber glass composite industry. This process begins with a release agent which is spray coated on the mold. This release agent ensures that the part will discharge from the mold smoothly.  Next the mold is gel coated with a pigmented polymer to give the part the specified color finish. Fiberglass is then added to the part either by the hand lay-up or spray-up process. The required thickness of the part determines how many layers of the fiberglass material will be used. Once the fiberglass cures, another layer of gelcoat may be added, if needed for the end product application of the part.

Advantages of this process are:
  • Minimal tooling and mold costs
  • Easy mold modification   
  • Design flexibility
  • Optimum for large production runs
  • Best range of large part sizes
  • Preferred for complex part
  • Mobile Modling

Hand lay-up is the simplest process and preferred for large parts. In hand lay-up the precut fiber pieces are placed on the mold and resin is applied to it. The MFG teammate will manually roll all of the entrapped air out of fiberglass, leaving a finished, smooth part.

Spray-up/Chopping is used often for large intricate parts. This process of spray-up the chop and resin flow through the chopper unit, and air pressure sends the resin mixture onto the mold through a spraying motion. As in hand lay-up, the teammate will roll out the air bubbles to get the finished, smooth part.

Open Mold Examples:
  • Locomotive ends
  • Military fuel cells
  • Hoods
  • Truck Doors
  • Truck Roofs
  • Rock guards for heavy trucks
  • Buildings
  • Tanks
  • Troughs
  • Track Pads


55 Fourth Avenue
Union City, PA 16438

(814) 438-3841


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Molded Fiber Glass Union City (MFG Union City), manufactured and shipped their 3,000th fuel cell for the military industry last month.