Made of treated foam rubber, dry sponges are used to remove dirt from any surface into which water or other liquids could soak and cause damage. Acoustic tile, artwork, and plaster walls are examples of such surfaces. Fold the sponge over and wipe the surface until the sponge no longer absorbs soil, then re-fold to use a clean section. Discard the sponge when it’s completely dirty. These products aren’t made to hold liquid, so do not try to rinse or use for wet sponging.
Don Aslett in The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros.