FONIRTE windows and doors have been tested to prove that the upvc used in the manufacture of our frames is self-extinguishing and will not hold a flame, making them a perfect choice for a safe home for you and your family. UPVC windows will not accelerate the spread of flames in the event of a fire as the chlorine content of the PVC acts as a fire retardant. UPVC window frames do not melt which is a common misconception based on how people perceive other plastic materials.