Piston rings are made of:

Piston rings are primarily made of steel due to its advantageous properties, which include strength, wear resistance, and the ability to withstand high temperatures and pressures within an engine. Steel has the necessary tensile strength to handle the forces generated during the combustion process, while also providing a good seal between the piston and the cylinder wall. This sealing capability is crucial for maintaining compression within the combustion chamber and for controlling oil consumption, which in turn affects engine efficiency and performance.

In terms of other materials mentioned, aluminum may be lightweight, but it lacks the necessary strength and wear resistance compared to steel, making it less ideal for piston rings. Cast iron is sometimes used for specific applications due to its resistance to wear and ability to handle thermal stress, but it is generally heavier and less flexible than steel. Plastic is not suitable for piston rings in traditional internal combustion engines because it cannot withstand the extreme conditions present during operation, including high temperatures and friction. Thus, steel is the most suitable and effective material for piston rings in most engine designs.