I'm banking IL is at least partially right. But I'm still figuring out what exactly sets off the ED molds, as I've had mixed results. Lately I've been using my smaller CC molds (which never blister). But just this past weekend I soaped in both my bigger white and red ED silicone loaf molds; both had some blisters, but only the red mold was significant (even then it was patchy). I actually thought it would be the other way around because I accidentally put the white loaf in a preheated (170 F) oven without first turning it off. I noticed that omission about 1/2 hour later, then promptly turned off the oven and cracked the door. About 10 minutes later I popped the red mold the same oven, which had by then cooled significantly. I did not use a thermometer to detect actual temps; instead went by skin feel.
The two batches were largely the same with the following differences (in my perceived order of importance):
insulation: the white mold was braced by a thin, partial plywood support frame (some of the mold was bare), whereas the red mold was taped shut in the original tight fitting cardboard box that it came in;
Base color: the white mold soap was yellow from beta carotene tinted coconut oil, whereas the red mold had normal CO for a natural base color
Other oils: were exactly the same except the white mold had 10% avocado oil whereas the red mold had 10% olive oil
Of those variables I think the insulation is the most significant culprit, with the FO following closely.
The blister results suggest the red mold overheated in the cardboard support despite the cooler oven temps, compared to the white mold.
I will admit that I have had more blisters in some previous batches in the white mold; not sure about particulars like insulation. I also know I have NOT gotten blisters in any of the few other red mold batches I've made. Also, I might as well add that red mold did not bleed onto the natural base colored soap of this batch, tho that did happen once before. I have no speculation on the difference in bleeding. Sorry for the lengthy post!