Cooling performance is good because aluminum dissipates heat 3 times faster than steel.

A steel sleeve is inserted as a lining in a conventional engine cylinder to protect the cylinder against abrasion from the piston. However, because steel has a poor heat dissipation rate that causes heat build-up in the engine, a better alternative to the steel sleeve has long been sought to improve performance. Yamaha answered this problem by making the aluminum cylinder itself so strong that it doesn’t need a steel sleeve. That is the DiASil Cylinder. It is an all-aluminum cylinder that achieves a high level of abrasion resistance on the cylinder wall by adding just the right amount of silicon granules to the alloy.