The Simple Way to Lose Weight
Although paper is usually specified in terms of weight (70 lb. text, 80 lb. cover), the printer and bindery consider paper in terms of thickness. A paper's thickness (or caliper) is an indication of the bulk, the heft, and the feel of the paper.
Uncoated papers are thicker than coated papers of the same weight, so you'll find you can get the same bulk with a lot less weight using an uncoated paper. For example, a 48 page catalog printed on a typical uncoated 60lb. text paper has the same bulk as a coated 80lb. text - yet weighs considerably less. The 60 lb. text sheet comes in around 4.5 oz. vs. 5.92 oz. on the 80 lb.coated sheet.
If your printed piece is going to be mailed or shipped choosing a lighter weight unocated paper can provide the bulk you want but will cost less for shipping and postage.