The warmer works in the same way as the gel hand-warming packs that warm up when you click a metal disc inside – when you press the orange button on the yoomi warmer, you’re effectively clicking the metal disc and it’s the phase change from liquid to solid inside the warmer that creates the instant warmth.
The cold feed is gently warmed as it flows around the specially designed channels on the outside of the warmer. By the time the feed reaches the teat, it is at natural breast milk temperature (32-34 deg C). The warmer has been carefully designed to stay warm for up to one hour. You then need to recharge the warmer between each use. You need to take the warmer back to its liquid state inside, ready to use again.