I pick up these sheers whenever I find them. The fiber content varies, often nylon/lycra or poly/lycra. These are fabrics that can come in handy for different projects. I use them for neck bindings, edgings, and sleeves. Sometimes I use them double, or as a layer on top of another fabric to mute it or kick back a color.
In my own studio, I stockpile these fabrics in colors I wear often.