The stand-up pouch found its origin in 1968 by Louis Doyen. That pouch design, including many variants, is still in use and is, in fact, the most dominant style of stand-up pouches.
The basic Doyen design consists of two flat sheets seamed together along their sides, with a “W” fold running along the bottom and sealed to the tube wall with an upside-down U-shaped area.
When the pouch is filled, the “W” (also called gusset) opens and provides a circular base on which the pouch can stand. The original Doyen design showed the top being sealed straight across, but subsequent modifications include fitments of all sorts.