Southwire Company 500 ft. Solid Building Wire with TFFN Wire Type and 18 AWG Wire Size, White

Thermoplastic flexible nylon (TFFN) fixture wire is a coated wire typically run through raceways that is specifically designed for fixture wiring. It's primarily used in commercial applications to power hardwired light fixtures in ceilings and walls. It's more flexible than THHN building wire but less resistant to heat, and it is only available in limited gauges (18 and 16 AWG).

Building wire and cable carry electrical current from a power source to a device in a building, such as an outlet or light fixture. Building wire is typically run through conduit, cable trays, or raceways. Building cable consists of multiple strands of wire bundled inside a thermoplastic or metal sheath. Building wire and cable are typically used to run new circuits or extend old circuits inside walls and ceilings in commercial, industrial, and residential properties.