Touch both objects. They’re the same temperature, but the wood feels warmer, right? Why is that? It’s not about temperature but thermal energy. When your hand touches an object, there is a heat conduction interaction. Energy is transferred from your warmer hand to the cooler object until the two are the same temperature. However, with the metal block it takes way more energy to reach the temperature of your hand. It feels cooler because it causes your hand to lose more energy.
You’ll notice the same thing when you go swimming. An air temperature of 75°F feels nice and comfortable, but wading into water of the same temperature feels really cold. That’s because water has a much higher mass and specific heat capacity than air, which causes you to lose more thermal energy and feel colder.
All Blankets Cool
So, blankets, how do they work? A blanket is basically an insulator. That means it prevents energy transfer between objects at different temperatures. Wrapping yourself in a blanket on a cold day keeps you from losing body heat to the air around you, so you feel warmer. Similarly, if you put a blanket around a cold soda on a warm day, it will slow down the transfer of thermal energy from the air to the soda, keeping the soda cold longer.
But what if you feel hot and you put on a blanket? In that case, two things can happen at once. It can still act as a thermal insulator and slow down the transfer of energy between you and the air. Unless the ambient air is above 98.5°F, this is going to make you hotter, not cooler.
However, the blanket can also have a thermal interaction with your body. Suppose you have a 80°F blanket in contact with a 98°F person. This will raise the temperature of the blanket while reducing the thermal energy of your body. Yes, it will act as a cooling blanket—at least for a few minutes, until the temperatures are equalized.
So, what makes one blanket cool more effectively than another? First, it should have a high mass, so that it takes a lot of energy to warm up. Second, the blanket needs to make good contact with your skin to increase the thermal interaction. So, one of those light fluffy blankets won’t cool you off that much. Other than that, it’s just a normal blanket.
But I’m a sucker for trying these things, so I bought a cheap “cooling blanket” online. (I know, someone will say it doesn’t work unless you get an expensive one.) For those who say their cooling blanket was out in the sun and they measured a 75°F temperature, I don’t believe you. Check this out. I have three blankets on my sofa. One of them is the cooling blanket and the others are normal. In back is the same picture taken with an infrared camera so that different colors represent different temperatures.
