Key characteristics of these flasks include:Insulation: Double-walled vacuum construction typically keeps drinks hot or cold for 12 to 24 hours.Capacity: Most standard models hold approximately 500ml (17oz).Material: Made from food-grade stainless steel (often 304 or 316 grade) for durability and corrosion resistance.Features: They often include a removable tea infuser or filter and a leak-proof screw lid.