Do You Need an Underlay With a Washable Rug?

With a woven non-slip backing, usually not. There are two situations where one still helps and one where it hurts.

What an underlay actually does

Three separate jobs, and people conflate them: it stops the rug moving, it adds cushioning underfoot, and it protects the floor from abrasion. A non-slip backing does the first. It does not do the other two.

When to add one

• You want more cushioning than a low pile provides.
• The rug is going over fitted carpet, where a non-slip backing does not help — carpet creep needs a carpet-to-rug gripper instead.

When not to

• Over underfloor heating. An underlay adds thermal resistance on top of the rug's own, and the two together can exceed what the system is specified for.
• Where you want the rug to lie as flat as possible under a door.

The one to avoid

Solid rubber or PVC underlays can react with a floor finish and leave a permanent discoloured patch, particularly on lacquered wood and vinyl. If you use anything, use a felt or a felt-and-natural-rubber pad, and lift it occasionally to let the floor breathe.