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Today, we will explore several commonly overlooked aspects of office paper. Why are there three primary paper size series-A, B, and C? How is paper weight measured? Is thicker paper inherently superior to thinner paper? And why does standard office paper typically come in a 70g/m² weight?
In practice, most commercially available paper consists of thin sheets made from plant fibers and is generally categorized by sheet count. Paper can be broadly classified into several types: letterpress printing paper, newsprint, offset printing paper, coated paper, book paper, dictionary paper, copy paper, and board paper. Each type serves distinct industrial applications and meets specific functional requirements.
01 Paper Size Standards
In 1786, German scientist Georg Christoph Lichtenberg (July 1, 1742 – February 24, 1799) discovered that rectangles with an aspect ratio of √2 exhibit favorable geometric properties. In the early 20th century, Walter Porstmann applied this principle to develop a standardized system of paper dimensions, which was formalized as the German DIN 476 standard in 1922. As adoption spread internationally, this system became the basis for ISO 216, the current international standard.
Paper specifications refer to standardized dimensions after cutting. Historically, paper sizes were denoted by "kai" numbers (e.g., 8-kai or 16-kai). Today, international standards define sizes such as A0, A1, A2, B1, B2, A4, and A5. These designations specify precise dimensions based on a consistent width-to-length ratio of 1:√2. For instance, A4 paper is widely used in offices, while A5 is common for medical prescriptions. Design and printing industries frequently use larger formats such as A3. The diversity in size reflects varying application needs, necessitating appropriate selection based on practical requirements.
02 Paper Weight and Basis Weight
Paper weight, or grammage, refers to the mass per unit area, expressed in grams per square meter (g/m²). Common copy paper typically has a grammage of 70 g/m², whereas photo paper often ranges from 120 to 150 g/m². Higher grammage corresponds to increased thickness and durability, which must be considered in relation to printer feed mechanisms.
The standard grammage range for paper spans from 25 g/m² to 250 g/m². Most office paper is conditioned under standard humidity and temperature conditions (23°C, 50% relative humidity) to ensure accurate measurement of its quantitative value.
A ream traditionally consists of 500 identical sheets; the total weight of such a ream is known as its ream weight. Alternative systems exist, including reams of 480 or 1,000 sheets, particularly in international markets. However, the industry primarily relies on grammage-the weight per square meter-as a key technical parameter. Grammage influences critical performance characteristics such as tensile strength, opacity, and print quality. While higher grammage enhances ink absorption and print clarity, it also increases ink consumption and production costs. Therefore, optimal paper selection involves balancing performance and cost-effectiveness.
03 Paper Materials and Applications
The six most commonly used office paper types include copy paper, letterpress paper, newsprint, offset printing paper, coated paper, and photo paper. With growing environmental awareness, recycled paper-produced through secondary processing of post-consumer waste-has become increasingly prevalent in office environments.
Copy paper, although designed specifically for photocopiers, is compatible with laser printers, inkjet printers, and multifunction devices, especially when high output fidelity is not required. It is particularly well-suited for general office printing tasks.
Letterpress paper is primarily used for printing books and periodicals. It is suitable for academic publications, scientific literature, textbooks, and educational materials. Based on raw material composition, it is classified into four grades: No. 1 to No. 4, with lower numbers indicating higher quality. Its fiber structure is more uniform than newsprint due to improved pulping and bleaching processes. Additionally, fillers and sizing agents enhance its printing adaptability, whiteness, and water resistance. Letterpress paper exhibits uniform texture, minimal linting, slight elasticity, good opacity, and adequate mechanical strength.
Newsprint, also known as white paper, is primarily used for newspapers, magazines, and comic books. It features low density, high elasticity, and excellent ink absorption, ensuring sharp double-sided printing. Calendering produces a smooth, lint-free surface. However, due to its high lignin content from mechanical pulp, newsprint degrades over time-yellowing and becoming brittle-and has poor water resistance. It requires low-viscosity inks and careful moisture control during offset printing.
Offset printing paper is used for high-quality color printing, including picture magazines, brochures, posters, and premium book covers. Classified into Special Grade, No. 1, and No. 2 based on pulp content, it is available in single- or double-sided finishes, and in super-calendered or standard forms. It offers low elasticity, uniform ink absorption, high smoothness, tight formation, good opacity, whiteness, and water resistance. Offset resin inks with moderate viscosity are recommended to prevent powdering or linting. Anti-offset measures such as powder spraying or interleaving are often necessary.
Coated paper is produced by applying a layer of pigment coating to base paper, followed by calendering. This results in a smooth, bright surface with even fiber distribution, consistent thickness, low elasticity, high water resistance, and excellent ink receptivity. It is ideal for printing albums, covers, postcards, product samples, and color labels. Printing requires controlled pressure and the use of resin-based or glossy inks. Back trapping prevention methods include anti-offset powders or interleaved sheets. Coated paper is available in both single- and double-sided variants.
Photo paper is designed specifically for photographic printing, requiring precise thickness, rigidity, color vibrancy, and long-term color retention. It features a specialized coating that enhances brightness and rapidly fixes fine ink particles, preserving image quality. The surface is rigid, supporting high-resolution output and minimizing ink bleed. Variants include glossy, textured, matte, professional, and self-adhesive photo papers. Glossy photo paper is common for home use, while self-adhesive types are used for ID photos and labels.
Recycled paper refers broadly to any paper produced using recovered fibers from waste paper, replacing virgin wood pulp. Industrial recycled paper often uses waste kraft paper, while cardboard liners may use mixed waste paper. Recycled cultural paper-used for writing and printing-is manufactured from deinked, bleached waste pulp. According to the U.S. Environmental Protection Agency (EPA), paper must contain at least 50% post-consumer fiber to be labeled as recycled. Currently, China lacks a national standard defining recycled content thresholds.
04 Use of Additives in Paper Manufacturing
During paper production, pulp fibers naturally exhibit a yellowish to grayish hue, which cannot be fully corrected by bleaching alone. To achieve higher whiteness, optical brightening agents (OBAs), including fluorescent whitening agents, are added. These compounds absorb ultraviolet light and emit visible blue light, enhancing perceived whiteness.
However, OBAs degrade over time due to oxidation, leading to yellowing of the paper. Although they provide short-term brightness enhancement, their instability makes them unsuitable for applications requiring long-term color accuracy. Key limitations include: (1) chemical interaction with inks that may compromise color fidelity, and (2) progressive loss of whiteness after exposure to light and air, making consistent color reproduction difficult.
OBAs are commonly used in high-whiteness papers such as copy paper, coated paper, and photo paper. Due to the inherent color of recycled fibers, OBAs are also frequently employed in recycled paper production. Notably, photo paper includes chemical coatings designed to stabilize ink and preserve color gradation, whereas other paper types lack such calibration capabilities.
Why is 70g/m² the Dominant Specification?
As discussed, even a simple product like copy paper involves complex considerations in material selection and manufacturing, influenced by production feasibility, raw material availability, and user preferences.
While heavier paper generally commands a higher price, 70g/m² copy paper remains the most cost-effective option. Thinner paper risks ink show-through, while thicker paper increases costs and reduces portability. Through extensive practical evaluation, 70g/m² has emerged as the optimal balance between durability, print quality, and economic efficiency.
With rising demand and industrial-scale production, economies of scale have reduced the manufacturing cost of 70g/m² paper below that of alternative weights. Consequently, this grammage has become the dominant choice for office environments.
Summary: Though seemingly mundane, office copy paper embodies a convergence of engineering, economics, and environmental considerations. We hope this article provides valuable insights into the science and standards behind everyday office materials.
