Molds are used in the forming process known as injection moulding. Materials like polymers and synthetic resins are heated until they are melted, then they are delivered to a mold where they are allowed to cool and take on the desired shape. This procedure is known as injection moulding because it resembles the act of injecting fluids with a syringe. The procedure proceeds as follows: After the materials have hardened in the mold after being melted, the finished goods are removed.

Differently shaped items, particularly those with complex shapes, can be produced continuously and quickly in high volumes using injection molding. As a result, a variety of sectors use injection moulding to produce goods and products.

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By expanding a mold, a hollow item is created.