Prior to 1845, before the invention of the first mechanized envelope creating machine, they were made by hand. The first commercial envelopes were created by Madison Verde, in 1876.
Making an Origami Envelope
There are primarily three types of envelope designs, that are used as templates by designers. They are known as kite, rhombus, and short arm cross designs. All of them involve the folding up of paper sides to create a rectangular envelope.
Here are simple and straightforward instructions on making one out of paper sheets. This design is called 'Rhombus'. For that, you will need a plain sheet of paper, pencil, scissors, glue, and a scale, along with some spare time that you can devote to this project.
Mark the Middle Point of a Square Paper Sheet
Get a square paper sheet. Before you can begin folding it, you need to locate the exact middle point of the square. To do so, fold the diagonally opposite corners of the square paper to the center, in such a fashion, that the resulting folded triangles, have their bases exactly parallel to each other.
Mark the point i.e. the apex at which these two folded triangles meet, as the midpoint of the whole square sheet of paper. Alternatively you could determine the center through measurements, using a scale.
Begin Folding Side Corners
After marking the midpoint, fold the two diagonally opposite corners again like before and finalize the folds. Press a scale on the bases of the two folded triangular corners, to create a clear crease.
Fold the Third Corner and Stick It
Leave the upper corner and fold the bottom corner towards the center, such that the corner lies well above the marked midpoint and above the meeting point of both side corners.
Again crease the fold using a scale. With that, your envelope is ready. All that remains is sticking the bottom fold, with the side folds.
With that, a rectangular enclosure, with an upper flap will be created, that we call an envelope. Some people use double tape to stick the bottom flap but glue can do the job for you. Just close the upper flap to ready it for use.
Make an experimental envelope first and practice till you get it right. Once you think you are adept enough, create as many as you want. With enough practice and by referring to a size chart, you will be able to make sleek, well folded, and finished commercial products.
To make tougher versions, use card paper, instead of thin paper. If Christmas is coming up, you can create fancy envelopes using colored paper, for sending greeting cards.