Abstract: A reversible underlay device for positioning between a rug and an underlying flooring surface to inhibit movement of the rug relative to the underlying flooring surface. In a preferred embodiment, the device includes a relatively resilient, conformable layer adjacent to a relatively firm layer having a plurality of outwardly extending nibs or protrusions. When a rug is placed over carpeting, the underlay may be oriented between the rug and the carpeting such that the nibs penetrate into the carpeting and the relatively resilient, conformable layer is adjacent the underside of the rug. When the rug is placed over a relatively hard flooring surface such as wood, tile or vinyl, the underlay is oriented between the rug and the carpeting such that the nibs penetrate into the back of the rug and the relatively resilient, conformable layer is against the flooring.