When a rug is on a hardwood floor, it is important to have the right rug pad underneath. The floor can experience damage from rug scratches and furniture indentations and the dense pad will prevent this from happening. 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. A quality rug pad will act as a barrier between the carpet and the floor to prevent any scratching from the back of the rug to the floor. Therefore, the carpet pad should be solid as opposed to one with holes in it. The more solid and dense the pad, the better the protection to the hardwood floor.
For rugs that do not tend to slip, a 100% felt jute pad is excellent. This is dense enough to protect the floor from scratches and indentations. Make sure that the felt rug pad is a 40 ounce, referring to the amount of fiber there is per square yard of pad. The higher the ounce, the more dense the carpet pad. 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.
I hear many people tell me that their pad stuck to their floor and it cost them a lot of money to re-finish the floor. The type of pad that does this is an open weave waffle looking pad. It may look and feel like rubber but it actually is a plastic or nylon pad that has a chemical spray applied to it. This chemical is what transfers to the floor and leaves an imprint of the rug pad right on the floor. Real rubber does not harm the floor and a felt and natural rubber carpet pad will prevent slipping and protect the floor.
It is always best to buy a solid pad when it comes to any hardwood or wood floor. 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.