With the increasing trend towards green roofs for both residential and business properties, flat roof insulation board in the format of EPS panels offers a perfect combination. Combining compression strength and lightness, EPS panels are available in densities from 10psi to 60psi. This means installation can be done quickly and gives designers and architects the benefit of both insulation and lightweight void fill. All this at a much more affordable cost than extruded polystyrene. See a successful project being completed step by step here https://www.universalconstructionfoam.com/projects/green-roof-construction/