| An envelope is a packaging product, usually made | | | | mail). Some envelopes are designed to be reused |
| of flat, planar material such as paper or | | | | as the return envelope, saving the expense of |
| cardboard, and designed to contain a flat object, | | | | including a return envelope in the contents of the |
| which in a postal-service context is usually a letter | | | | original envelope. The direct mail industry makes |
| or card. The traditional type is made from a sheet | | | | extensive use of return envelopes as a response |
| of paper cut to one of three shapes: the rhombus | | | | mechanism. |
| (also referred to as a lozenge or diamond), the | | | | Up until 1840 all envelopes were handmade, each |
| short-arm cross, and the kite. These designs | | | | being individually cut to the appropriate shape out |
| ensure that when the sides of the sheet are | | | | of an individual rectangular sheet. In that year |
| folded about a delineated central rectangular area, | | | | George Wilson in the U.K. patented the method of |
| a rectangular-faced, usually oblong, enclosure is | | | | tessellating (tiling) a number of envelope patterns |
| formed with an arrangement of four flaps on the | | | | across and down a large sheet, thereby reducing |
| reverse side, which, by virtue of the shapes of | | | | the overall amount of waste produced per |
| sheet traditionally used, is inevitably symmetrical. | | | | envelope when they were cut out. In 1845 Edwin |
| When the folding sequence is such that the last | | | | Hill and Warren de la Rue obtained a patent for a |
| flap to be closed is on a short side it is referred | | | | steam-driven machine that not only cut out the |
| to in commercial envelope manufacture as a | | | | envelope shapes but creased and folded them as |
| '"pocket"' - a format frequently employed in the | | | | well. (Mechanised gumming had yet to be devised.) |
| packaging of small quantities of seeds. Although in | | | | The convenience of the sheets ready cut to |
| principle the flaps can be held in place by securing | | | | shape popularized the use of machine-made |
| the topmost flap at a single point (for example | | | | envelopes, and the economic significance of the |
| with a wax seal), generally they are pasted or | | | | factories that had produced handmade envelopes |
| gummed together at the overlaps. They are | | | | gradually diminished. |
| most commonly used for enclosing and sending | | | | As envelopes are made of paper, they are |
| mail (letters) through a prepaid-postage postal | | | | intrinsically amenable to embellishment with |
| system. Envelopes are useful. | | | | additional graphics and text over and above the |
| Window envelopes have a hole cut in the front | | | | necessary postal markings. This is a feature that |
| side that allows the paper within to be seen. They | | | | the direct mail industry has long taken advantage |
| are generally arranged so that the sending | | | | of -- and more recently the Mail Art movement. |
| address printed on the letter is visible, saving the | | | | Most of the over 400 billion envelopes of all sizes |
| sender from having to duplicate the address on | | | | made worldwide are machine-made. The |
| the envelope itself. The window is normally | | | | envelope-machine making industry is dominated |
| covered with a transparent or translucent film to | | | | internationally by Winkler and Dunnebier. |
| protect the letter inside. In some cases, shortages | | | | Post office requirements |
| of materials or the need to economize resulted in | | | | Post offices prefer envelopes to be rectangular |
| envelopes that had no film covering the window. | | | | rather than square, as this reduces the amount of |
| One innovative process, invented in Europe about | | | | sorting that is needed to line up all the envelopes |
| 1905, involved using hot oil to saturate the area | | | | with the addresses reading the same way. |
| of the envelope where the address would appear. | | | | Australia |
| The treated area became sufficiently translucent | | | | In Australia, post office-preferred envelopes have |
| for the address to be readable. A typical use for | | | | four boxes printed in orange ink at the bottom |
| window envelopes is courtesy reply mail. | | | | right-hand corner where handwritten postcodes |
| An aerogram is related to a lettersheet, both | | | | are meant to be written. Character recognition |
| being designed to have writing on the inside to | | | | software is used to read the postcode number. |
| minimize the weight. Any handmade envelope is | | | | The Reply Paid is a system whereby a customer |
| effectively a lettersheet because prior to the | | | | may reply to a sender, with the sender bearing |
| folding stage it offers the opportunity for writing | | | | the cost. Specially printed envelopes are used, |
| a message on that area of the sheet that after | | | | with the sender's address and the words "Reply |
| folding becomes the inside of the face of the | | | | Paid" with an authorization number. The stamp is |
| envelope. | | | | replaced by three black stripes. The sender pays |
| The "envelope" used to launch the Penny Post | | | | the postage plus a fee to the postal authority. |
| component of the British postal reforms of 1840 | | | | The customer may write the Reply Paid envelope |
| was a lozenge-shaped lettersheet. But if desired, a | | | | out by hand. |
| separate letter could be enclosed with postage | | | | Other countries use freepost as well, although the |
| remaining one penny, provided the combined | | | | envelope designs required by those countries' |
| weight did not exceed half an ounce (about 13 | | | | postal authorities differ widely from that described |
| grams). This was a legacy of the previous | | | | above. For example, in the U.S., Reply Paid is called |
| system of calculating postage, which partly | | | | Business Reply Mail. |
| depended on the number of sheets of paper | | | | Envelopes in the Soviet Union were printed with |
| used. | | | | something like the common 7 segment LCD |
| A "return envelope" is a preaddressed, smaller | | | | display, to assist the user to write the |
| envelope included as the contents of a larger | | | | 6-character postcode directly in machine-readable |
| envelope and can be used for courtesy reply mail, | | | | format. |
| metered reply mail, or freepost (business reply | | | | |