db_What is the overall difference on the plastic when fully heated and then only at the critical points?
I have not been able to detect any damage to the plastic, the flex has remained the same. The way the boot looks now, it probably won't last another 5 seasons :-).
As I said, the heel was fine until a few days ago, so I assume it's the liner and I just need a small solution. As suggested by onenerdykid.
Spot punching is generally a higher temperature for a lesser amount of time. Boots that are designed for molding heat at a lower temperature and cool down faster and tend to be thinner plastics. Boots not designed for it need higher temperatures to mold (or at least to be heated for longer), and increases the risk a handful of issues such as ovalizing your buckle holes, warping the plastic, etc. You're right that it's probably just the liner, and you may just need some foam around the heel. But i reiterate, heating the entire shell up, especially without any pressure from an outside source (like Fischer's older vacuum fit system), will generally cause the entire shell to expand. This
could be part of why your heel feels looser now. Does that make sense?
tomPietrowskiIf a boot is made from PU it can be heat molded. it may take longer to cool to keep the shape but there is no reason you cannot mold any PU boot.
Agreed. As I said, some boot brands/models aren't "made" for it. I never said it isn't possible. If PU wasn't moldable, punching them wouldn't work so well