Premium Flask Quality: The premium flask is 304 (18/8) stainless steel with laser welded joints. Also, the premium quality flasks are individually leak tested using a pressurized air and water system. The body of the flask is .5mm thick and the actual weight is almost doubled that of the standard flask. When quality and value matter most you will want to choose the premium quality flasks; they make great gifts! Due to the nature of custom made products no returns, exchanges or refunds are offered.