Paper Thickness Weight Information
Paper is available in a wide range of thicknesses and weights. Understanding the differences is often the key to selecting the best paper for your project. It's also important to understand that when it comes to paper, thickness and weight are two very different aspects.
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Considerations
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Different weights and thicknesses of paper are used for various projects. Thicker paper is more durable, but depending on what you're creating, it can be a detriment. For example, when you are printing post cards, you'll want to select a thick stock so your cards will stand up to the rigors of postal equipment; but if you're manufacturing a textbook, that same stock will be too thick and thus a poor choice.
Basis Weight
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Paper is categorized by its basis weight. The basis weight is the weight of 500 sheets (one ream) of the paper in its basic or parent size. It's important to understand that different types of paper have different parent sizes. The parent-size sheet for cover stock measures 20 by 26 inches. If a paper is referred to as 65-pound cover, it means that one ream of it in its basic/parent size weighs exactly 65 pounds. On the other hand, typical office paper is 20-pound bond. In its parent size (17 by 22 inches), one ream weighs twenty pounds.
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Caliper
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Caliper is the actual thickness of a sheet of paper and is expressed in thousandths of an inch. The thickness is measured with a micrometer. The size of the sheet has no bearing on its caliper. The caliper of a sheet of 65-pound cover will be the same--within a five percent acceptable variance--whether the sheet is in its parent size (20 by 26 inches) or cut to a post card size of 4 by 6 inches.
Equivalent Weights
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Determining the best paper for your project can be confusing because a number of different types of paper have equivalent weights, although their designations make them sound very different. For instance, 20-pound bond is an equivalent weight to 50-pound offset. You would think the latter would be heavier and thicker, but offset paper has a much larger parent size than its bond counterpart, so its weight designation sounds heavier. The caliper of these two sheets is nearly identical.
Postal Card Stock
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As paper is sold by weight, heavier stocks cost more. The same is true with mass mailings: heavier pieces cost more to mail. For this reason, many paper manufacturers have created a stock specifically designed to be thick enough to meet the postal regulations for caliper but lighter than its standard paper equivalent. Sometimes called "high-bulk" or "7-point reply," this paper is unusually light for its thickness and rigidity.
Opacity
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Thicker papers are also more opaque. Opacity is an important consideration when printing on both sides of the sheet. Less opaque sheets often create readability problems, since you can see the image on the reverse bleeding through. When manufacturing books, using a thicker stock to gain opacity is not always an option since your book would be too thick and too heavy. To alleviate this issue, choose a stock that is designated as an "opaque." Opaques have the same weight and thickness as their bond or offset counterparts, but they are manufactured specifically to reduce "show-through." Therefore, you can select 50-pound opaque for textbook pages and will get the opacity benefit of a heavier paper without compromising the overall weight and thickness.
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