The quality of the mould is very important and dramatically effects the quality of the product.
Moulds have common features for whichever of the processes they are used for. Moulds can be wooden forms to bend acrylic accurately or complex metal moulds.
Surfaces must be hardwearing and well finished. Moulds can be textured so that the plastic is formed with the texture in the surface.
Moulds must be sloped to allow the plastic product to be lifted off or pulled out. The slope is called a draft angle, it should be between 5-10 degrees.
Corners should have a radius on them to allow better plastic flow. Sharp corners lead to an area of stress and weakness and can split the plastic.
Any recess in vacuum forming moulds must have small vent holes drilled in to prevent trapped air stopping the plastic sheet from forming.