I once drove three miles squinting through a two-inch clear patch at the bottom of my windshield. It was raining. I was late. The defroster was on full blast and somehow making it worse. I pulled over, wiped the windshield with my sleeve — which just smeared the fog around — and sat there wondering why a machine with three hundred horsepower could not clear a piece of glass.

The problem was not the defroster. It was me. I was using it wrong. Here is what I learned after that miserable drive — and what has kept my windows crystal clear ever since.

Step One: Turn On the AC (Yes, Even in Winter)

Fog forms on the inside of your windshield because warm moist air hits cold glass and condenses. Your breath is the main source of moisture. The defroster blows warm air at the windshield — which helps — but warm air alone cannot remove the moisture.

Turn on the air conditioning along with the heat. Set it to the windshield defrost setting. The AC compressor pulls moisture out of the air before it reaches the glass. The heat keeps you comfortable. The combination clears fog faster than either one alone.

I know it feels wrong to run the AC when it is forty degrees outside. Do it anyway. Most modern cars automatically engage the AC compressor when you hit the defrost button — check your manual. If yours does not, press the AC button manually.

Step Two: Crack a Window

Open your window about half an inch. It lets humid air escape and replaces it with outside air — which, even when raining, is usually drier than the air inside a car with four people breathing. You will feel a draft for thirty seconds. Then the fog clears and you can close it.

The Cat Litter Hack (Prevention)

Fill an old sock with silica-based cat litter — the crystal kind, not the clumping clay kind. Tie it closed. Tuck it under your passenger seat or in the rear footwell. The silica absorbs ambient moisture from the car’s interior, preventing fog from forming overnight.

I keep one under each front seat during winter. Swap them out every couple of months or when you notice fog returning. It is the same principle as those little silica gel packets in new shoes — just scaled up. Total cost: about three dollars for a bag of litter that will fill four socks.

Clean Your Windows. Seriously.

A film of dirt, vape residue, or dashboard off-gassing on the inside of your windshield gives moisture something to grab onto. A clean window fogs less. Use a dedicated glass cleaner and a microfiber cloth — not Windex and paper towels. Windex leaves a residue. Paper towels leave lint. Clean both the inside and outside once a month during foggy season.