The best rug pads for hardwood floors are ones that are either a solid felt or a felt and natural rubber combination. When a rug is walked on, there is pressure to push through the rug and hit the floor. The more solid and dense the pad, the better the protection to the hardwood floor. If the rug tends to slip, then a felt and natural rubber rug pad is ideal. Here, the key is to make sure it is natural rubber as opposed to the chemical sprays that look and feel like rubber but actually could severely harm the floor. It may look and feel like rubber but it actually is a plastic or nylon pad that has a chemical spray applied to it. Take care in making sure that if it is a 100% felt pad, the felt is recycled without any chemicals or adhesives. If it is a non slip felt and rubber rug pad you need, make sure the rubber is actually a natural rubber and not a rubber like substance that can harm the floor. Read more about carpet flooring.