[rbanffy]

I was going to say blood of virgins, but tears are probably better heat conductors.

[ciupicri]

I tempted to say that blood is better one. Among other things blood has iron, while tears just salt. Last, but not least it's for thermoregulation of the body.

[snovv_crash]

If we're evaluating blood and tears for cooling, I'd argue that sweat is significantly better as a renewable resource, and also specifically adapted towards evaporative cooling.