If a woman finds a stain on a surface that is not mekabel tumah (susceptible to ritual impurity), then that stain does not make her niddah.

We follow the view that fabrics made of 100% synthetic materials, such as polyester or nylon, are not mekabel tumah. If the rov (majority) of the fabric is synthetic, opinions differ regarding its status. There can be room to be lenient with stains in such a case, and a halachic question should be asked. If 50% or less of a material is synthetic, then the fabric is mekabel tumah.

Rayon and viscose are a special case, since the materials are derived from plants before processing. We would ordinarily consider them to be mekabel tumah, except perhaps in very extenuating circumstances.

If you are purchasing sheets, we suggest purchasing colored sheets for non-niddah times, since stains on colored surfaces are generally treated leniently, regardless of the fabric content.

Updated 13 November, 2025.