Factors affecting the formation of insulin amyloid spherulites

► We study the tendency of insulin to form amyloid spherulites and fibrils. ► We report a statistical method to estimate the balance of spherulites and fibrils. ► Spherulites are the dominant aggregation pathway at low pH and protein concentration. ► Protein concentration affects the balance between free fibrils and spherulites. ► pH changes around 2 largely affect the final spherulite size.