There is are lot of holes on the fins for efficient ventilation.

This is the K8 retention clip for the HR-01 heatsink.

Beside that, the 120mm fan duct which is special design to use with the HR-01 heatsink is also available to purchase separately. This 120mm fan duct is most suitable for those chassis that having the 120mm fan size at the rear side to intake the hot air from the heatsink directly blow out from the chassis.