i have read from many places the evidence that shims decrease cooling performance, but they gave no explination. Haven't seen this anywhere so I am going to post my hypothesis on why this is. Almost every shim i have seen for sale have been made of copper. Most heatsinks and waterblocks are made of aluminum. Now, the heatsink conducts heat away from the cpu and throughout the baseplate of the heatsink and is then supposed to conduct heat into the fins. But the heat never makes it to the fins, cause the copper to absorb it. The copper just absorbs more and more heat until finally it starts conducting heat back down into the cpu, thus amounting to the increased tempetures. Now going with this hypothesis, if a shim were made of a substance that did not conduct heat, and was resistent, say some plastic, performance should stay the same, while being safer for the cpu core.