Metals have very high heat transfer coefficients.<p>In cold weather, the heat that usually conducts from your head to warm a plastic interior is instead being instantly transmitted to the environment.<p>With a cold spot right next to your head, it acts as a condensation point for a water that is always being emitted from the human body. (A fun experiment you can do in dry cold weather is hold up a warm finger to a window and watch condensation immediately appear even at a distance.)<p>The design is especially prone to this failure mode in the dead of winter when you have the highest temperature gradients.<p>Because these aren’t waterproof, I doubt they did much testing outside where you would experience such large deltas in temperature.