Thermal resistance estimates are very approximate and NOT measured. I removed 1 star because radiator manufacturers should provide this information and should not force customers to find out for themselves. In addition, they did not provide information on the thickness of the base and plumage. I measured about 3mm base thickness and 1mm rib thickness. There were also a few minor rough edges in the base (didn't really factor that into the ranking as a bit of sandpaper should take care of that). Personally I wouldn't use this for a Peltier cooler, I don't think it's big enough. I want to use it for some MOSFETs.