They do contain polypropylene. Why: Our top sheet does not include cotton - cotton is actually one of the least effective available top sheets for a pad as it absorbs liquid and does not distribute it away from the skin. This has been the problem with most mass produced "natural" pads. A cotton top sheet is similar to a cotton t-shirt in that it doesn't wick moisture away, but rather stays soggy once wetted. Currently, our non-woven is a best-in-class fusion of short and long fibers that are "entangled" to produce a moisture-wicking dynamic.