Stainless steel hip flasks are not designed to keep drinks cold for an extended period. Stainless steel is a good conductor of heat, which means it doesn't insulate well against external temperatures. Therefore, if you pour a cold drink into a stainless steel hip flask, it will eventually reach room temperature due to the heat transfer from the surrounding environment.
However, stainless steel flasks may provide some short-term insulation, helping to maintain the initial temperature of a cold beverage for a brief period. But they are not as effective as insulated containers specifically designed for keeping drinks cold, such as thermoses or vacuum-insulated bottles.
If you want your drinks to stay cold for longer periods, it's better to use a dedicated insulated container designed for that purpose. These containers are typically double-walled and vacuum-sealed, providing superior insulation to keep beverages cold for several hours.