Why do I need HEAT SAFE? Heat Safe is the essential protective and reparative spray for heat-styled hair. Why does HEAT SAFE rock? Sultra’s heat-activated ThermaStress® Complex mends and defends the hair and creates a protective, anti-fading seal around hair. Repair, smooth and strengthen hair—all while you style! How do I use HEAT SAFE? Lightly spray sections of hair when ironing or blow-drying.