Non-skid rugs pads
Pads beneath area rugs are needed primarily to keep a rug from sliding or moving. Even rugs with heavy furniture on them can slide around when they are on top of hard surfaces (wood, stone, tile, vinyl, linoleum, etc.). Sometimes a thick pad is used to make the rug feel thicker or softer or even to bring up the height of a rug to meet an adjacent surface. In some instances, a rug pad can be attached to a rug, when it is being fabricated from broadloom carpet.
It is important to note that because a non-skid rug pad is meant to resist movement over the floor that it, or the rug, can get bunched up (rippled) if furniture is pushed or slid on the rug. The ripple or bump in the rug can become permanent if it is walked on too much, creating a flattened crease.
If you experience this bump or ripple it is advised to remove the furniture and roll the rug up as tight as possible, then roll it back out. Tugging the rug to take out a ripple can damage the rug or, at best, just bunch up the pad beneath it. If a ripple appears to be stubborn and regular rolling won't take it out then it could be necessary to not only remove the furniture but to also flip the rug over and roll it inside-out (reverse-roll). This can re-stretch the backing of the rug to match the surface. Leaving the reverse-rolled rug alone for a few hours can give it enough time to even out the front and back.