I haven't used the PSK foil, but I've tried foil right out of the box. Both regular and heavy duty Reynolds. The regular did start leaking faster than the heavy-duty, but in the end, they both didn't get to boiling.

In all fairness though, it may have been cuz I was setting them on the gas range, like any other pot. I haven't tried a campfire with the cup sitting on a rock or something that would better distribute the weight.