The Envelope: History, Production, and Future of Paper Packaging

Background

A modern envelope is a flat, flexible paper container with a single opening sealed by a flap. Sealing methods vary: traditional wet‑taped flaps, metal fasteners, string‑wrapped cardboard inserts, and the latest adhesive‑strip envelopes that require no moistening.

Envelopes are almost always rectangular, available in a wide spectrum of sizes. The two most common styles are banker envelopes—opening on the long side—and pocket envelopes—opening on the short side. In the United States, standard dimensions range from 3.5 × 6 in (89 × 152 mm) to 10 × 13 in (254 × 330 mm). European sizes span 3.2 × 4.5 in (81 × 114 mm) to 11 × 15.75 in (280 × 400 mm), while the UK commonly uses 4.25 × 8.625 in (108 × 219 mm).

Some envelopes feature windows cut into the front to display interior addresses. These windows are often protected with a transparent film.

History

The concept of a sealed container dates back to ancient Babylon, where clay tablets were baked and then covered with a second clay layer that could only be broken to reveal the message.

True paper envelopes emerged only after paper itself was invented. Papyrus—made from the fibrous stems of Cyperus papyrus—was first produced by the Egyptians around 3000 B.C. It remained a primary writing material across Egypt, Greece, Rome, and the Arab world until paper from other sources reached Europe in the 12th century.

Chinese papermaking began with reeds and rice around 1200 B.C., and by 105 A.D., Ts'ai Lun introduced a superior mix of mulberry, hemp, rags, and fishing nets. Paper spread westward, reaching Baghdad by 793 A.D. and, by the 14th century, several European countries—Spain, Italy, France, and Germany—had established paper mills. The 1450s printing press dramatically increased demand for paper.

Paper envelopes likely appeared in China early on, but they were not introduced to Europe until the 17th century, when Spain and France began mass production. Even today, some stationery is folded and mailed without an envelope.

Initially made from cotton and linen rags, paper shifted to wood pulp in the early 19th century, coinciding with mechanized papermaking. Karl Marx noted the industry in Das Kapital (1867). Production grew from 3,000 envelopes per hour in the 1860s to over 50,000 per hour by the late 20th century. In the 1990s, the United States produced nearly 200 billion envelopes annually.

Raw Materials

Most envelopes are paper‑based, though large, heavy‑duty envelopes may use synthetic polymers like polyethylene, derived from petroleum‑based ethylene.

Envelope paper is typically wood pulp, but high‑quality invitations may incorporate cotton or linen. Manila paper, originally from the leaves of a Philippine plant, is now usually wood‑based but retains the name.

Two adhesive types are used: a consumer‑side gum (often gum arabic or synthetic dextran‑based gums) and a stronger backing glue derived from starches (corn, wheat, potatoes, rice). Fasteners may be aluminum or other metals; string fasteners use cotton or other fibers; window covers are commonly polystyrene.

The Manufacturing Process

Making Wood Pulp

• Mechanical pulping yields weaker paper suitable for newspapers; envelopes require chemical pulping.
• Common chemical method: Kraft pulping—wood chips are digested in a heated, alkaline mixture of sodium hydroxide and sodium sulfide at 160–180 °C and ~116 psi for 0.5–2 hours.
• Bleaching removes lignin through successive oxidizing steps, followed by alkaline washes.
• Fillers (e.g., kaolin clay) and additives (starches, gums, rosin, alum) improve brightness, opacity, smoothness, and sizing, preventing ink bleed.
• The pulp is poured onto a mesh screen, drained, and pressed through rollers to remove moisture, then dried by heated cylinders.

Making Paper

• The pulp slurry is laid on a fine‑wire mesh. Water drains, forming a wet sheet.
• Rapid‑spinning rollers create a partial vacuum, extracting more water.
• Moving belts of felt absorb water and protect the sheet while it passes through 40–70 steam‑heated rollers.
• Calendaring smooths the sheet; it is then wound onto a reel. Envelope paper typically has a basis weight of 16–40 lb/ream, with 24 lb being common, and is usually uncoated.

Making Envelopes

• Paper rolls (~220 lb/100 kg) are fed into automated machines. Sheets are cut into diamond‑shaped blanks to minimize waste.
• Blanks are folded, glued, and, if needed, windows are cut and covered with transparent film.
• Strong glue secures the envelope’s structure; a weaker glue is applied to the flap for consumer sealing.
• Optional printing, fasteners, or adhesive strips are added before the envelopes are boxed and shipped.

Quality Control

Automated production yields consistent products, but key checks ensure reliability: paper weight, envelope dimensions, glue placement, print accuracy, and window precision. Sample envelopes are inspected for defects and conformity to specifications.

The Future

While envelope design is unlikely to change drastically, papermaking is evolving. Innovations focus on efficient, cost‑effective, and environmentally friendly production. Advances in genetic engineering may produce faster‑growing trees with pulp properties tailored for envelopes. Increasing use of recycled paper will likely continue, reducing raw material consumption and environmental impact.