plication

... its a word, look it up... So I wanted to write a letter to a friend, but I didn't have a letter, so I wrote the letter and thought i could try to make one. so I did, and It fits the letter really well. Look at the pictures

going from left to right.

line up letter to the center of paper

fold edges over letter

put letter on bottom of paper and fold to make crease. 

open paper and make triangle fold so that the lips above the line are close and the lips below open

fold paper closed with letter inside the closed lips.

close open lips on back side.

fold bottom of paper up over the lips on the backside, a flap should remain

fold flap of paper into pockets.

you have an origami envelop customized for your letter.

This works best if letter is thinner then actual envelop