What is a Rear Window Demister?
Clears your back window on frosty mornings in under a minute
Simplified animation — not to scale.
In plain English
The rear window demister — also called a heated rear screen — is a grid of thin horizontal electrical strips painted onto the inside surface of your rear window. Press the button and they warm up, melting frost and clearing condensation so you can see through your mirror clearly.
"Picture a radiator turned sideways and shrunk down to fit on your back window. The horizontal lines are like the hot pipes of a radiator, each one gently warming a strip of glass so the whole surface clears evenly."
How it works
The grid lines are made from a conductive silver-based compound baked onto the glass during manufacturing. When you press the demister button, current flows through these horizontal strips and they act like tiny heating elements. The warmth radiates across the glass, raising its temperature enough to melt ice and evaporate moisture. Most systems include a timer that automatically switches off after about ten to fifteen minutes to prevent overheating and save battery power.
Signs of trouble
- ⚠Grid lines not heating up when the button is pressed
- ⚠Only some grid lines working, leaving cold stripes on the glass
- ⚠Demister turning off too quickly or not at all
- ⚠Scratched or peeling grid lines visible on the glass
- ⚠Blown fuse every time the demister button is used
£150 to £400 for full rear window replacement with new heating elements
Always get a written quote. Prices vary by car, region, and parts brand.