I used thin strips of a plastic juice concentrate can wall
They're exactly of the correct thickness (just about 0.1 mm lower than the core) and come at absolutely no cost (you won't have risk sacrificing a Radeon for your OC
). All you need is scissors, some glue ("superglue" i.e. cyanoacrylate is just fine) and an empty, thoroughly rinsed juice concentrate can.
Goes without glue as well, but some care must be taken when seating the HSF or waterblock or vapoelement or whatever you're using
Seating and reseating moves things easily thus risking the contact: if a strips goes over the tiny "spiders" soldered onto the processor base and the heatsink/whatever is attached without double checking everything, the first boot after the procedure will burn the poor chip since there's very little or no contact between the core and the cooler. (Yes, been there...)