With a polyboard cover the guide can be placed in more strenuous environments and exposed to temperature extremes. The polyboard cover is perfect for guides that will be used in non-climate controlled areas, or that will be traveling with someone.
The white side is used for bouncing light back into the shadows of an image, for example a light would be placed on one side of the model and a white polyboard on the other side of them. The light would illuminate one side and the polyboard would fill in the shadows from the other side providing a very beautifying light.