Bicomponent fibers are defined as fibers produced by extruding two different polymers from the same spinneret, allowing both polymers to coexist within a single filament. This innovative structure provides unique properties that neither polymer could achieve on its own. A related term, "co-spun fiber," refers to filaments made from different polymers, with each filament containing only one component.

In some regions, particularly in Asia, the term "conjugate fibers" is used interchangeably with bicomponent fibers. The primary goal of creating bicomponent fibers is to harness the distinct capabilities of each polymer to enhance performance and functionality.

One notable example of bicomponent fibres is those constructed with a polyethylene sheath surrounding a polypropylene core. These fibers are crucial in the nonwoven fabric market, offering benefits such as improved durability, resilience, and thermal bonding properties.