Vortex-RC 5mm Biofoam Depron Extruded Polystyrene Foam Sheets 30"X20" Size 10 Sheets. Depron is a brand name for Extruded Polystyrene (XPS) closed cell foam in sheet form, It is a fantastic medium for building model aircraft, and also a popular medium for architectural model building, as well as model boats and prototype design, XPS foam is stronger than traditional EPS Themocol and can be further strengthened with carbon fiber or wood strips. Strength to weight ratio and rigidity is perfect for RC airplanes Easy to cut with precision by knife Easily sandable Sheets are flat and have a smooth finish.