Why is tie dying so popular?

Tie dye is the Word used to describe using several colors to dye a piece of fabric at once. Shirts, Bags, etc. with swirled or circle patterns meant to look hand painted are often associated as tie dye since they resemble the real thing.

It's considered popular since it has been used globally- dating back to 500 AD- as a cheap and quick way to color blank fabrics- usually cotton- in any color(s) of the designer's choice.