Opacity levels - and what it actually means

Quick facts

LOWER OPACITY LEVELS

HIGHER OPACITY LEVELS

Double sided printing is likely to show a bleed through of text and images with lower opacity levels

Ideal for double-sided printing as printed text and images are less likely to bleed through to the other side. Photo papers have a relatively high opacity (94-97) compared against ordinary papers, so bleed-through is less of an issue

General Overview:

Opacity is expressed in a percentage, and is a measurement for the degree of light transparency of the paper. Paper which lets a lot of light through is transparent, while a paper which lets less light through has an opaque value. The higher the value, the more opaque the paper is. So, if you hold up a piece of paper up to a light source if it's so thick that light won't shine through it, then it's opaque.

Opacity isn't always determined by thickness or weight since a thinner paper may be more opaque than a thicker one. The more fibres or fillers in a paper, the more opaque it will be. Thinner papers can be made more opaque with opacifying thickeners. (For example Bible paper is a thin but opaque paper which is made from 25% cotton and linen rags or flax in combination with chemical wood pulp. This grade of book paper typically has a long life and is durable and strong).

Test Methods include:

TAPPI T-425 - quantifies the opacity of paper by testing a sample of normally ten 8.5" x 11" sheets of paper using 89% reflectance backing.

Paper and Media