insulation help

[jspfore20]

IN wire, what does the F in TFFN stand for. Any help would be appreciated.

 

[paul]

Thermoplastic Insulated, Flexible, Fixture, Nylon Jacket Conductor - TFFN (Stranded)

Thermoplastic Insulated, Fixture, Nylon Jacket Conductor - TFN (Solid)

 

[bphgravity]

Thermoplastic Insulation, Flexible Fixture wire, Nylon jacket