EPS panels are treated with an effective, non-toxic additive that will deter insects. The additive is environmentally sound and contains no dyes, formaldehyde or ozone-depleting HCFC’s. The additive is inert, non-nutritive, highly stable and therefore will not decompose, decay or produce undesirable gases or leachates. The insect-resistant foam panels are recyclable and safe for waste-to-energy systems and landfills. The treatment is a process which uses a natural mineral formulated to resist normally occurring exposure to woodboring insects, specifically carpenter ants and termites. The non-toxic treatment is EPA Registered, meets the standards of ASTM D3345 and WPA EL 12-72, and lasts as long as the rigid insulation.