Control-line models are built of the same basic materials and construction methods as R/C and free flight models. Control-line model construction varies with the category of model. Aerobatics and combat models are relatively lightly built compare to R/C models as they need high maneuverability in the limited space offered by the control line hemisphere. They are typically built with traditional materials like balsa wood, plywood, paper, plastic, spruce, and polystyrene foam, but modern composite and graphite/epoxy are occasionally used in high-load applications. Combat models must also be relatively easy and quick to build, as mid-air collisions and crashes are common.