It's 240W so the heatsink needs to be big in order to dissipate the heat effectively. The cooler a COB is the more efficient it is (up to a point), and the bigger the heatsink is the cooler the COB will be (up to a point). My heatsinks also have a convection current cooled core. There's water in the core, encased in the aluminum cylinder. The water vapor carries heat up to the top of the heatsink, then releases it, condenses and drops back down. Like a lava lamp. This helps distribute the heat evenly throughout the heatsink, so the fins can dissipate it more effectively. Compared to the heatsinks I tested that were purely aluminum it runs about 15F cooler at 240W.
-Keith