These diapers do not smell chemically like others, such as Costco diapers. Which I highly do NOT reccomend. They are pretty much the safest diapers you can get in my opinion and they are very transparent on the packaging what they use. For example, they do use polypropylene. However, this is the safest plastic material on the market and significantly better than materials such as polyurethane etc. They also control leg blow outs better than most diapers. Not 5 out of 5 as I wish the back was a tad longer or layered better to control blow outs that go up the back.