If the ice is thick, sometimes I still throw a bit or warm water on the screen as it's quicker but the heated screen stops it freezing.

Back in the sixties, when I endured several Canadian winters, and car heaters were pretty primitive, especially on the Morris 1100 I drove, one could buy pieces of plastic sheet about A5 size with a self-adhesive edge. It was essentially a piece of double-glazing. Fairly useful on a side-window but it didn't really like being wound up and down inside the door.

I also tried smearing high-boiling alcohol such as dodecanol on the screen, which worked quite well for a few days. (from the lab of course ....)

Edited by Andrew-T on 14/02/2022 at 18:46

A suitably flattened corrugated cardboard box is very effective in reducing/eliminating frost accumulating on a windscreen.

Don't know if it is any good yet as I have not tried it, but I bought some de-icer the other day. It claims to be a 'two in one' product which. if you know it is going to be frosty, you just spray it (and leave it) on the windscreen the night before which (they claim), prevents the frost from forming. But you can also use it as a normal de-icer.