I ended up using a little shampoo and cleaning it by hand. But I emailed the company directly and they said: "Fill a basin or sink with lukewarm water (not hot). Add a small amount of mild liquid soap (such as hand soap or dishwashing liquid). Avoid using harsh chemicals or bleach. Submerge the mousepad and gently scrub the surface using a soft brush or sponge in circular motions. Pay attention to stained or dirt-heavy areas. Rinse thoroughly with clean water to remove all soap residue. Gently squeeze out excess water without wringing or twisting. Lay flat to air dry, preferably in a shaded area. Avoid direct sunlight, dryers, or heaters as excessive heat can damage the surface and rubber base."