Do washable area rugs lay flat or do they curl at the edges?

Verified-purchase reviewers and specialist subreddit threads report mixed results. Most low-pile washable rugs lay reasonably flat, especially the heavier 8x10 and 9x12 sizes with TPR/rubber non-slip backing. However, multiple r/HomeDecorating commenters note that lighter, thinner rugs can be too light to vacuum without shifting and may need a separate rug pad to stay put.