Universal Foam

Expanded polystyrene foam is also a great void filler. It has been used on multiple pools. If you want to see examples or find out more information about that you can look at http://univfoam.com/construction/eps-geofoam-for-swimming-pool.

If your looking for a lightweight void fill under the concrete portion of the pool, its a great way to ensure that the pool is long lasting with less problems in the long run. If your looking for further information, you can go to http://univfoam.com/construction/eps-geofoam-for-swimming-pool to see how it was done in the past. Hope this helps!