Plastic frames are the cheapest to produce. All plastic frames are injection moulded by a machine that heats the plastic until it's molten then squirts it into a precise mould which when the plastic has cooled again, bingo you've got a frame component produced - very cheaply. Thats the good side of plastic frames. The not-so-good side is that plastic frames have a tendency (compared to the similar material acetate) to lose shape over time. Its not so easy for getting beautiful colours into the frame unless its painted on and this creates the possibility of it flaking or wearing off eventually, but hey they're cheap!
Acetate is a nylon-based plastic that is strong, lightweight and flexible. It is also hypoallergenic. Acetate glasses have the largest range of transparency, rich colours and finishes as it can be produced by layering several colours or transparencies and laminating them together.
Acetate eyewear is then made by combining layers of plastic into large blocks, the individual parts are then cut from it. It is hand polished and finally assembled into a complete frame.Because of the extra work involved, and also the extra colour possibilities, acetate is always used for more expensive eyewear brands. It retains its shape and colour for longer than plastic, but is more expensive.
