EPS (expanded polystyrene, white bead foam) is cheap, light and easy to cut — great for big parts, cores, masters and packaging; its bead structure leaves a slightly coarse surface. XPS (extruded polystyrene, the coloured insulation board — pink/blue/green) is denser, stronger and cuts to a lovely smooth edge — ideal for wings and fine work. Both hot-wire beautifully.
EPP und EPO are moulded bead foams used for durable, flexible RC models; they are tougher and more rebound-y but do nicht hot-wire cleanly (they melt/gum rather than slice) and are usually moulded, not cut. For hot-wire work, think EPS for cheap and big, XPS for clean and strong; leave EPP/EPO to moulded parts.
EPP und EPO are moulded bead foams used for durable, flexible RC models; they are tougher and more rebound-y but do nicht hot-wire cleanly (they melt/gum rather than slice) and are usually moulded, not cut. For hot-wire work, think EPS for cheap and big, XPS for clean and strong; leave EPP/EPO to moulded parts.