You won’t find a better flask out there! Anodized inside and out for corrosion resistance and a rugged billet aluminum body, o-ring sealed for leak-proof protection. Custom colors available. The most notable feature—these are eXpandable! Available in 5-ounce and 8-ounce sizes, we have eXpansion kits to expand your 5-ounce X-Flask to a maximum beverage-toting 8-ounces and back again (6.5-ounce X-Flasks available for corporate branding and branded gifts)