When casting a part or mold, their mass density will have a large impact on polymerization time.
Indeed, the exothermic reaction produced by a two inch thick mass will be higher compared to one only 1/8th of an inch (0.125), which will effect greater reactivity of the molecular chain as well as faster polymerization. Since the exothermic reaction takes place in the centre of mass, this heat will remain in the casting and will therefore yield a shorter polymerization time.
In a 1/8 of an inch (0.125) mass, the lesser exothermic reaction tends to leave the mass and therefore slows down the reactivity of the molecular chain, which causes the polymerization time to be much longer.