Opacity affects readability

Opacity is the characteristic of paper that prevents printing on one side from showing through to the other. Opacity affects readability. High opacity helps readers concentrate and reduces confusion and eye strain, and also prevents photos, screen tints, or reverses on one side of a sheet from showing through to the other side. Many characteristics affect opacity. Generally speaking, thick paper is more opaque than thin, coated more opaque than uncoated, rough more opaque than smooth, and dark more opaque than light. Swatchbooks usually don’t include opacity ratings; it is best for you to decide whether a sheet is opaque enough for the job by inspecting it rather than knowing its rating. You can increase opacity without increasing basis weight by using slightly darker paper. Often you can change from white to ivory or light gray without increasing costs, and this strategy might raise quality substantially in the case of a directory or catalog.