One that exceeds the wind chill temperature in your area, probable the orange/yellow stuff.
Take a low actual temperature thats equal to or less than the temperature of the windshield washer fluid and spray that on a windshield moving down the road it will freeze. Outside temp -5, washer fluid of -20 and a wind chill of -30, you have a frozen windshield.
i usually use some cheap vodka and i dye it what ever color i want, it never freezes.:shifty: