Bottles with a screw-off bottom are not suitable for the bottle mode because as they have otften silicone valves that can not remain in the water for such a periode of time. Plastic valves are no problem. Additionally, keeping food warm for long durations can impact its quality. However, water can be kept warm in bottle mode, and you can pour the warm water into the Mammafeel bottle along with the food for easy and quick access, especially during nighttime feedings.