The base of metal-plastic windows – the profile – is made of a special fire-resistant material of polyvinyl chloride (PVC). The PVC made of a profile includes special additives (for example, chlorine), they prevent the possibility of ignition of plastic during the fire in the room (the index of flame propagation for PVC windows is zero).
In other words, the window plastic will not support the burning process, while the wooden window will flash instantly, like a match. If during the fire the room temperature jumps to 200°C, the window plastic can only melt, but no more. In addition, many window makers install insulated glazing units with good insulation properties, so they do not burst from heat, which in turn prevents the flow of oxygen into the room.