Vacuum all four sides of the pillow-top mattress, using the non-bristle vacuum hose attachment. This will remove any dirt that has collected on the surface of the mattress.
Mix 1 cup of laundry detergent with 5 cups of water in a bucket.
Wet a clean rag in the detergent/water mixture. Wring the rag out so that the rag is damp, but not dripping.
Scrub the mattress with the damp rag so that the cleaning solution can attack any buildup in the mattress fibers. Avoid excessively wetting the mattress by scrubbing the entirety of the surface evenly.
Place the mattress in direct sunlight and allow it to dry completely. If the mattress does not dry completely, you run the risk of mold setting in.