Paper weight is an important consideration in selecting fine stationery. In the United States, paper density is measured in terms of pounds (”#”) for a given quantity of uncut paper and in grams for most other countries of the world. For instance, paper for copy machines is generally 20# (twenty pounds). This measurement term was determined long ago as the weight of 500 sheets of uncut paper at a paper mill. Another mill-term that pops up occasionally is “two- or three-ply paper. “ This refers to sheets of 32-pound paper that are joined together to make heavier paper stock. For instance, 3-ply paper is the equivalent of 96# paper.
The best way to determine the paper weight that works best for you is to “feel it and bend it.” In general, quality letterhead stationery weighs between 24# to 32#, fold-over notes weigh 64# and card stock weighs between 96# and 120#. Formal invitations for weddings and Bar/Bat Mitzvah can weigh anywhere from 96# to 240# depending on the effect you are seeking to obtain. Also, you frequently see different colored paper stock mounted on top of each other to create a layered effect for wedding and Bar/Bat Mitzvah invitations.
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This fascinating site reveals the traditional methods of making various types of prints.
A well beaten/refined pulp, short fiber pulp such as hard wood or straw pulp,highly filled or loaded paper will show lower thickness for given basis weight.