I have always heard and read about how warm wool blankets are, but when I bought a brand name blanket to use at home, I found that I have never slept colder under any other type of bedding in my life. Is there something wrong with my blanket or is wool more marketing than substance?
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TL;DR Wool blankets function differently than duvets or comforters. They are better in a lot of ways but you need more of it for the same affect.
Any form of bedding insulation works by trapping air. Heat is just particles moving really fast, and warm air particles are moving particularly fast. Cold air doesn’t move as fast, but if it interacts with hot air, it steals some of the heat energy from the hot air so it can move faster too (thus becoming warmer)
The air around your body takes heat from you in order to move faster. And when it does that it usually moves faster *away* from you, where it crashes into other air particles and gives those air particles some of the heat that came from you. Feeling cold is basically air stealing heat from you to give it to all its air-friends.
Bedding and insulation work by trapping air and stopping it from passing on its energy to its air friends. Instead it just has to bounce around next to you with nothing to give its extra energy too. Ever wrapped yourself in plastic wrap? Did you get really sweaty real quick? Air can’t move through plastic wrap, but your body needs to be able to give *some* of its extra energy to the air or you get too hot – and start sweating.
Polyester bedding is quite similar. It’s literally made out of plastic. You don’t need a lot of Polyester to block air movement because it’s quite dense. But that thin-and-dense quality that blocks the air from being a heat thief makes it really easy for water to be a heat-thief. Water is much faster at stealing heat from you, and also has a much easier time at passing it across a thin barrier. If you get too sweaty and it’s humid outside of your bed, you can start to loose heat again. (This is also why you get so cold quickly after a workout even on a warm day, lerformance fabrics are all made outbof polyester)
Wool is different. Wool doesn’t block air, it just throws up a really complicated obstacle course. Particles will eventually get through it, but how long that takes depends on how big the obstacle course is. Because of that, you need more wool to properly block air from running away with your heat faster than your body can produce it. But because it’s an obstacle course and not a barrier, air that runs away with your body heat *also* runs away with your sweat particles. And because you need more of it to be effective, the quality that makes it really hard for air to find its way out also makes it really hard for water to find its way out. So if you get too sweaty, you’ll still keep water from stealing your heat at the same time you’re stopping air from stealing it. (This is why thermal clothes for tramping are made out of merino wool)
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