Most photographic prints produced today are made on resin-coated paper. The manufacturers coat paper with a plastic resin, then apply a light-sensitive emulsion to the top of one side of the paper. Fiber paper is 100% cotton without the resin coating, resulting in a light-sensitive emulsion that is saturated in the cotton fibers. This yields an image with more depth and a broader range of tones than an image printed on resin-coated paper. When placed side by side with a resin-coated print, a fiber print will exhibit a richer image under identical development.
A properly processed fiber print stored or displayed in appropriate conditions will last for centuries. The plastic in a resin-coated print emits gasses that will likely degrade the print over the same time span.