I am on luremaking hiatus currently. My last casting was of the 9" plug and I spray painted it but did not it epoxy it. It has been sitting in plug bag in car and is getting fished. Haven't caught on it. But no cracks. I flex it every once in a while. There is a quite a bit of flex. And no cracks showing.
RideHPD: 1) the 36hrs cracked one was not subjected to car heating it went into car on the same day as I went fishing and it was a cool day to start with. 2) All the plugs have spent a number of days in car, some more than others. 3) I love your analysis ideas. I will refer to them should the etex thing and trying a new batch of the resin does not result in the problem being resolved. I'm ordering some more foam soon. Alumilite kindly offered me 25% coupon.
Here's the picture Anglingarcher requested. The foam was purchased directly from Alumilite, not via Amazon.