The Women’s Bamboo Knit Panty Kit is a Rayon fabric made of the natural fibre from bamboo. It is naturally cool in summer and warm in winter. I cannot imagine there are many fabrics more comfortable year round than bamboo rayon. Since it is a natural fabric, we advise pre-washing it prior to use. If you find that it curls while you are working with it, a good shot of spray starch, sometimes called Fabric Sizing (found in the grocery store) will tame it.