Most people are surprised to learn geofoam is flexible to the point that it can be used for retaining wall backfills and even buried wall backfills. Rely on geofoam for backfilling behind the retaining walls on your property and you will significantly decrease the lateral pressure. This is possible as geofoam has such a light weight. Though geofoam is quite light, it has an inherently high compressive resistance, making it perfect for retaining wall backfills and other buried structures. Keep in mind the pressure placed upon a retaining wall is dictated by the weight of the backfill.