It is best not to submerge any stiff foam pillow in water. Instead, you could just wipe off the surface with a clean cloth. You could even wash the cover if at all, it is removable. But you can choose to wash the pillows with softer coverings and fillings in washing machines. Make sure you put them on a gentle cycle cleaning process. You could also air dry them. This way, you could maintain its fluff and preserve its shape. Apart from this, it is always better to check the laundry tag on the pillow to follow the correct washing process.