A heavy frame is the structure of the largest ships and stations: frames reinforced with exotic alloy, raw exotics and composite, put together in an Assembler. The flagship, deep miner, bulk hauler, ark and leviathan are built with heavy frames, and so are the anchorage, the defence battery, every heavy thruster and ring segment, and fittings such as the compressed hold.
In research, its high melting point steers a design toward more fuel capacity, mining rate and power output, at the cost of cargo capacity.