The S/S and S/S PRO straws are made of medical grade 304 stainless steel, making them strong, durable, and corrosion resistant. Steel is a sustainable material that is infinitely recyclable and easy to clean & sterilize. The PRO adds an anodized finish on the straws as well as an aluminum case to further complement the sleek form factor. We prioritize recyclable materials with recycled content in our packaging and shipping elements.