Since this thread popped up again it reminded me I should give a quick update on the No-Melt Mylar I used as a liner (link in Post #11):
It's true, as advertised it didn't melt, but the side pieces did warp. I tried them twice, once as a CPOP with the soap put into the oven at 170F and turned off, and then once with the soap just sitting on the counter wrapped in blankets. In both instances, this particular product warped along the sides, creating big waves. The recipe was the same both times, and no "super heater" ingredients (i.e. honey, spicy EOs, high CO content, etc) were added, although the usual lye concentration I use is 38-40%.
Still trying to find the perfect adjustable liner, but regardless, love having his mold on hand!