Shimano Deore XT disc rotor with Ice Tech technology. The key to Ice Tech is a piece of aluminium sandwiched between the steel external bits. The aluminium draws the heat away from the external steel allowing for greater braking capacity on large downhill rides.

.Replacement Deore XT 180mm brake rotor . Ice Tech '3 layer Stainless/Aluminium/Stainless' for efficient cooling and better performance . Compatible with resin and metallic brake pads 
SHIMANO ICE TECHNOLOGY disc brake rotors and pads reduce heat buildup and provide consistent and reliable braking power available. The rotors feature a 3-layer stainless steel-aluminum-stainless steel sandwich design that radiates heat for better performance. The brake pads have an aluminum radiating fin that helps dissipate heat throughout the system.
Together, ICE TECHNOLOGY rotors and brake pads deliver a quieter ride while reducing brake fade and extending pad life for a more reliable and confident riding experience.