I used cotton material I already had and lined it with material from an old cotton sheet which was thicker. Some recommendations are to leave an opening and add a filter of non woven material (a coffee filter was suggested). As this one is pleated it may give an extra bit of protection. The ones pictured below were made from cotton curtains that I no longer use.
Note: If you don't have elastic, two pony tail holders can be used for children.
T-shirts can be used instead of elastic
With supplies of elastic running low because of the Corona virus pandemic, the video below shows how to make one using clothes line rope.
