15:56 16-11-2025

Rear window defrosters: from anti-fog films to modern heated glass

Modern cars clear fog from the rear window at the push of a button, but it wasn’t always like that. Back in the 1960s, German engineer Heinz Kunert was the first to propose heating with conductive filaments, yet many models right up to the late ’70s didn’t offer it. For those, there was a curious add-on — a transparent anti-fog panel sold in cardboard tubes and stuck to the inside of the glass.

On paper, the film was meant to prevent condensation and improve visibility in damp or cold weather. Real-world impressions varied. On Morris Minor forums, owners recall that it did nothing and that fitting it was an ordeal. Others note the film would darken, curl at the edges, and eventually fall off.

Even so, some classic-car fans maintain it worked and helped them on trips. Given the age of surviving panels, though, expecting much today seems optimistic — the adhesive layer and the plastic have long since degraded.

As technology moved on, the accessory faded away, displaced by auxiliary electric glass heaters and fully integrated heating sections. Today, if a car lacks a factory defroster, universal kits priced at $89–359 are available; they operate on the same principle as the heating wires embedded in modern glass. For most owners, that’s the simpler way forward.