Polycarbonates are strong, stiff, hard, tough, transparent engineering thermoplastics that can maintain rigidity up to 140Ã‚Â°C and toughness down to -20Ã‚Â°C or special grades even lower. The material is amorphous (thereby displaying excellent mechanical properties and high dimensional stability), is thermally resistant up to 135Ã‚Â°C and rated as slow burning. Special flame retardant grades exist which pass several severe flammability tests. Constraints to the use of PC include limited chemical and scratch resistance and it's tendency to yellow upon long term exposure to UV light. However these constraints can be readily overcome by adding the right additives to the compound or processing through a co-extrusion process.