Abstract: Disclosed are curable epoxy-based resins having a lower peak exotherm during cure, as well as thermoset resins and epoxy-based parts formed from the curable epoxy-based compositions. The epoxy-based compositions having a lower peak exotherm during cure may include: at least one epoxy resin, at least one hardener, and at least one endothermic transition additive. The thermoset resin may include the reaction product of the curable epoxy-based resins having a lower peak exotherm during cure, which may be useful when forming large epoxy-based parts, such as those including 200 grams or more of the thermoset resin. Also disclosed is a process for forming curable epoxy-based resins having a lower peak exotherm during cure, including: admixing at least one epoxy resin; at least one hardener; and at least one endothermic transition additive; to form a curable composition. The resulting curable composition may then be thermally cured at a temperature of at least 60° C. to form a thermoset resin.