Zn phosphinate, organo-modified sepiolite and poly(ethylene terephthalate) (PET) have been melt blended to develop a new flame retardant system for PET plastics and textiles. The combination of Zn phosphinate and sepiolite have been exploited in order to enhance the flame retardancy of PET for both plastics and textiles. The thermal stability of PET blends evaluated by thermogravimetric analysis and differential scanning calorimetry results remarkably affected by the loaded fillers. The combustion tests by cone calorimetry reveal a relevant decrease of combustion rate and a high increase of fire performance index for both plastics and textiles due to the presence of this novel flame retardant mixture. Analogously, limiting oxygen index has been found increased in a remarkable way.