Most of the glare from nonmetallic surfaces is polarized,

Question

the axis of polarization being parallel to that of the reflecting surface. Would you expect the polarization axis of Polaroid sunglasses to be horizontal or vertical? Why?

Answer 1

The polarization axis of Polaroid sunglasses should be vertical.  This axis would reduce glare more effectively.

Mathematically speaking, you want to make cos^2(theta) between the incident light and the polarization axis as close to zero as possible.  The way to do that is to take theta as close to 90 degrees as as you can.

Since the light is polarized horizontally (parallel to the reflecting surface), we want a vertical polarization axis.

Hope that helps!