Composite materials (mainly is resin and fiberglass fabric or fiberglass mat) are placed in an open mold, where all materials will cure or harden while exposed to the air.
The product cost for open molds is often inexpensive, and easy to handling.
open mold process----Hand lay up process
The fiberglass reinforcement is laid into a mold which has been coated by a release agent and a gel coat. Then a resin mixture is used and pushed by a roller to release air bubbles. When the reinforcement is completely wet out, another layer of reinforcement is added and repeat the processes until the product gets its requested thickness. Then the product need to be cured at room temperature or under heating conditions.
Materials involved: chopped strand mat, stitch mat, woven roving, combo or combined mat, surface veil etc.
----Spray up process
Fiberglass roving is cut by a chopper and then sprayed together with resin mixture into a mold. Then a roller is used by hand to compact the glassfiber on the mold to release the air bubbles. The product is ready when it is cured.
Materials involved: spray up roving
The picture from JUSHI 
