de-ices a windshield – within seconds – with just a few wipes of a bag of hot water. Hot water in a zip lock bag and you’ve got a de icer and a hand warmer.

results vary with the amount of time the hot water bag is allowed to slowly pass over the ice. Too fast and not enough melting happens

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https://www.motoringresearch.com/advice/ultimate-de-icing-life-hack/