Waterlogged Styrofoam is a problem most commonly seen in hot tub and spa covers. The average life span of this type of cover is approximately one to three years, before the foam becomes waterlogged. Once the Styrofoam becomes waterlogged, it no longer can insulate properly. You will know if your Styrofoam is waterlogged because it will be much heavier than normal. The waterlogged Styrofoam can be repaired by drying in high sunlight, but it is cheap and more effective to simply replace the Styrofoam.
Take the Styrofoam out of the cover, or from the area in which it has been overexposed to water. Be sure to also remove any plastic covering that may be on the Styrofoam, as this will prevent the foam from drying out. It may take two people to lift the Styrofoam, as it will be much heavier from retaining water.
Lay the Styrofoam out in a dry and sunny area, and allow it to sit for several days. It is best if there is an area where the foam can sit on a slight angle so that some water may drain out.
Flip the Styrofoam over every other day so that both sides are exposed. Try this method for a week. If the Styrofoam does not begin to dry, it will be easiest to replace the old Styrofoam with new and place a new plastic covering over it. If the Styrofoam does dry, it will feel lighter; cover it with new plastic or vinyl covering.
Take the old Styrofoam, if any of it did not dry out, to a recycling plant that recycles Styrofoam. The Styrofoam may possibly be needed at boat docks. The Styrofoam can also be used in plants to help improve drainage.