Leggings, tank tops, swimwear, and exercise wear are all made of stretch knit fabric. Some are 4-way and others are 2-way stretch. Depending on what you’re producing, you will need to select the right amount of stretch in your knit fabric. Leggings and swimwear require 4-way stretch, while comfort wear may only need 2-way stretch. Comfort wear includes that shirt broadcloth shirt you just purchased. A shirt is not made to stretch, but to give additional comfort adding stretch will do that well.
Stretch fabrics were introduced to the world of fashion in the 1960s with discoveries by DuPont. Since that time, the world has embraced knits. Now, they have almost become the dominant fabric structure and in some categories of clothing have indeed accomplished that very feat. Stretch knit is now used to construct every piece of clothing known to man, including coats, socks, underwear, swimwear, pants, tops, shirts, skirts, dresses, culottes, shorts, you name it, you will find it made in a knit fabric.