Organic brake pads are so called because they consist mainly of various hydrocarbon compounds, products of organic chemistry. The matrix of synthetic resins holds the entire lining together in one piece. The fibres in the matrix give the brake pad mechanical strength. Various fillers (including metals) are used to determine useful properties such as the coefficient of friction. Up to 25 different organic materials can be used in a single brake pad. Sintered brake pads are named after their manufacturing process. Sintering is a process in which different materials (usually metal or ceramic), in powder form, are brought together under high pressure and high temperature - the result is a metal-like material. Sintered pads are generally harder and more wear resistant than organic pads. However, sintered pads are more susceptible to squealing, put strain on the caliper due to increased heat conduction (therefore not recommended for any brake) and are more expensive to produce than organic coatings. Incidentally, to function optimally, the discs must be matched to the type of pad. Generally, discs with a few small holes on the braking surface are suitable for the softer, organic pads, while discs with large holes on the braking surface are better suited to the hard sintered pads (see also: ceramic pads). Some brakes even work with both surface types. It can be easy to see which type of pad you have in front of you : most of the backing plates have one or more holes. If the material of the coating pad fills the hole, it is most likely an organic coating, if the hole is empty, it is a sintered pad which is glued on.