Unlike other leading brands, [proof] products are built using super high-grade MEDICAL GRADE STEEL. This means not only superior corrosion resistance, but products that will last longer. BPA free, so no plastic toxins to worry about. These water bottles are insulated using EcoProofTM technology, a non-toxic insulation technique that uses safe materials through our ENTIRE production process. No copper coatings, contaminants or other hidden insulating elements here. Keeps beverages cold for 24 hours and hot for 12 hours. 18 oz/532ml.