When it’s below 32 degrees F, you need three layers to stay warm. True or False. There’s no “always.” The number of layers varies widely from person to person, says Castellani. No matter how many you wear, they need to transport sweat from the skin to the air so it can evaporate. Water has 70 times the convective heat transfer of air, meaning that the same reason you want to be wet when you’re working out in the summer is the same reason you want to avoid it in the winter.