Simplicity and variation
Single chamber teabags in square shape, either with 4-edge sealing or folded and with 3-edge sealing, mark the origin of teabags anyhow. The filter paper ist not crimped but sealed, so a type of filter paper is needed which is capable of being treated this way. Due to the simple manufacturing process of the standard square bag the machines run faster and are much easier. And due to small consumption of filter material the bag is economic and cheaper.
There are however also possibilities of tube-forming filter paper creating other forms with much more space for the tea, and weighing the tea with the advantage of filling broken teas, leaf teas or coarse cuts instead of fine cuts.