Fenders, both original and replacement, can be made from one of several materials. Typically, original fenders are made from the same material as the car body, which, for most cars, means steel. Some cars, however, use aluminum bodies, and others are made with a steel structure and fiberglass or reinforced plastic body panels. Some manufacturers also use carbon fiber for body panels. Although this is currently limited to luxury vehicles, carbon fiber bodies may become more common over time. Replacement and aftermarket fenders can be made from the original material or a different material. Lightweight and reduce the weight of a vehicle, improving fuel economy and performance over steel. All fender materials have some tradeoffs.
One of the more common reasons to buy an aftermarket fender is to find one with a different shape. While some replacement fenders are the same shape and size as the original, others come in a variety of shapes tailored for specific uses. Custom-fit fenders are available smaller than stock, allowing the use of larger wheels. Other aftermarket fenders stick out more from the sides of the vehicle, providing more protection from rocks and mud and accommodating wider wheels. Fender flares can also be purchased and installed separately, bolted onto existing fenders. An extreme example of fender shape is the fender skirt, typically used on the rear wheels of front-steering vehicles.
Like most automobile parts, replacement fenders are available aftermarket or OEM. An OEM, or original equipment manufacturer, part comes directly from the manufacturer and is an exact replacement of the original part. This makes OEM parts reliable and easy to install, but they also tend to be more expensive. Aftermarket parts are made and distributed by companies other than the original manufacturer. The biggest advantage of buying aftermarket parts is choice; aftermarket fenders are available in a variety of materials, shapes, and price points. However, quality control in aftermarket parts can vary, so buyers should choose parts from reputable suppliers.
Another reason drivers purchase aftermarket fenders is to replace the stock fender for functionality or looks. Aftermarket fenders may be larger, to accommodate larger wheels, or flare out more for wider wheels. Aftermarket fenders may also be stylized to customize the look of a car's body.