Why put a pad under a rug at all?
A pad does three jobs: it keeps the rug from sliding, gives it a soft cushion that eases pressure on the fibres, and separates the backing from the floor so there is less scratching. Those three together extend the life of both rug and floor.
On smooth floors such as marble and porcelain it is a safety matter before it is a style matter, because a sliding rug can cause a fall for a child or an older person. So a pad is not a luxury.
But not just any pad will do. Material, thickness and size decide whether it protects or harms, and the next sections go through each.
