Key Features and PerformanceInsulation: These bottles feature a double-wall vacuum insulated construction.Temperature Retention: Depending on the specific model, they can keep liquids hot for up to 15–24 hours and cold for up to 20–24 hours. Some larger capacity variants claim retention for up to 72 hours.Material: They are typically fabricated from high-quality 18/8 stainless steel both inside and out, making them sturdy and unbreakable.Design: The flask usually includes a lever or flip lid for easy dispensing and a wide mouth for convenience. Some models also include a filter for brewing tea