Helps in the rain.
I did find that before the rain-x, when you might get morning dew on the back glass, it would collect in large groups and then run off the glass when you started driving. There was some visibilty to the rear through the water(hard to explain).
Now after rain-x, the morning dew would be broken into tiny droplets which didn't run off the glass because they weren't large enough in mass to get going down the low angle of the glass. And because the dew was distributed sort of evenly across the window and it actually hindered visibility like a mask. I started squeegy-ing my back glass on those 'dewy' mornings. Once the rain-x wore off, I didn't reapply for that reason
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