Do Not Wash Foam Cushions, Only Clean Stains
If you machine wash the pillows, they will look new and not yellow again . While we have advocated washing pillows properly before, this is not the case with foam pillows.
Good Housekeeping explains that to clean your foam pillows, you should vacuum or dry them in an air-only dryer to remove dust. Clean the stain off all soiled areas and allow to air dry. Also:
Some foam pillows come with hand washing instructions. If you choose to follow them, be very gentle. Wet foam is heavy and breaks easily. To keep your pillows clean longer, use a pillowcase liner and wash them monthly.
The above advice conflicts with some of Deadspin’s advice , but may depend on the type of foam cushion you have. When in doubt, just clean up the stain, as the foam cushions fall apart quite easily.
The Best Way to Clean Your Pillows | Good housekeeping