Eli5: How come wood stays cool to the touch in high temperature environments (e.g. saunas) when all other common materials would be hot?
In: 671
What you feel is not temperature, but heat transfer to and from your body. Wood isn’t very good at heat transfer. That means it’ll take longer to get hot from heat and longer to transfer heat to you. It also means that if it’s in contact with heat on one side, it’ll be cooler on the other side than metal for example.
Elianor’s answer is the right one, I just want to add WHY wood is a bad / slow heat conductor. Wood is mostly air, and air is a bad heat conductor, especially when it’s confined to a bunch of little pockets that can’t move or circulate to help move the heat. That’s how clothing, blankets, and even fiberglass and foam insulation work – it’s all about trapping tons of tiny air pockets, creating a material that passes heat very slowly since the energy has to hop from one pocket to the next to the next and all this transferring takes time.
Wood is a similar deal. Dry wood contains a ton of air confined in many little pockets, so it acts like a thermal insulator. That’s why it feels cool to the touch in the sauna – it’s at the same temp as the room, but it transfers that heat very slowly into your finger so it doesn’t feel as hot as metal at the same temp that quickly dumps heat energy into your finger. And that’s also why a wood toilet seat feels WARM to the touch. It’s just as cool as the room, but it transfers heat from your butt slower than plastic, so the wood feels warmer. Again it’s the rate of heat transfer (in or out!) that you feel, not the temp itself.
What you feel is not temperature, but heat transfer to and from your body. Wood isn’t very good at heat transfer. That means it’ll take longer to get hot from heat and longer to transfer heat to you. It also means that if it’s in contact with heat on one side, it’ll be cooler on the other side than metal for example.
Conductivity.
We normally think about that in electrical terms, but it’s very important in heat transfer as well.
Some materials, like wood do not conduct (transfer) heat well. Some (like water) are very good at it.
Elianor’s answer is the right one, I just want to add WHY wood is a bad / slow heat conductor. Wood is mostly air, and air is a bad heat conductor, especially when it’s confined to a bunch of little pockets that can’t move or circulate to help move the heat. That’s how clothing, blankets, and even fiberglass and foam insulation work – it’s all about trapping tons of tiny air pockets, creating a material that passes heat very slowly since the energy has to hop from one pocket to the next to the next and all this transferring takes time.
Wood is a similar deal. Dry wood contains a ton of air confined in many little pockets, so it acts like a thermal insulator. That’s why it feels cool to the touch in the sauna – it’s at the same temp as the room, but it transfers that heat very slowly into your finger so it doesn’t feel as hot as metal at the same temp that quickly dumps heat energy into your finger. And that’s also why a wood toilet seat feels WARM to the touch. It’s just as cool as the room, but it transfers heat from your butt slower than plastic, so the wood feels warmer. Again it’s the rate of heat transfer (in or out!) that you feel, not the temp itself.
Conductivity.
We normally think about that in electrical terms, but it’s very important in heat transfer as well.
Some materials, like wood do not conduct (transfer) heat well. Some (like water) are very good at it.
Go pick up a metal spoon. Then go pick up a wooden spoon (ladle/spatula watever)… the metal feels colder right?
But they have both been in in your house for a while and both at room temperature. However, the metal is far more conductive and can ‘steal’ heat from you faster than the wood can.
This also works the other way, hot metal can dump heat into you much more quickly than wood.
It’s slightly on topic, but kinda weird. Could this be why I find it comfortable knitting with wood or bamboo needles and metal needles hurt my hands and knuckles?
Go pick up a metal spoon. Then go pick up a wooden spoon (ladle/spatula watever)… the metal feels colder right?
But they have both been in in your house for a while and both at room temperature. However, the metal is far more conductive and can ‘steal’ heat from you faster than the wood can.
This also works the other way, hot metal can dump heat into you much more quickly than wood.
It’s slightly on topic, but kinda weird. Could this be why I find it comfortable knitting with wood or bamboo needles and metal needles hurt my hands and knuckles?
Latest Answers