Polycarbonates
are strong, stiff, hard, tough, transparent engineering thermoplastics
that can maintain rigidity at up to 140°C and toughness at down to -20°C
or even lower for special grades. The material is amorphous (thereby
displaying excellent mechanical properties and high dimensional
stability), is thermally resistant up to 135°C and rated as slow
burning. Special flame retardant grades exist which pass several severe
flammability tests.