Glass vs Plastic (Surface Feeling)

[meisamkh]

Hello All

 

I have a question about the cold touch of the glass versus the warm touch of the plastic.

 

As we know it is not because of the heat conductivity as glass has very low heat conductivity. It is speculated that the difference is because of heat capacity of glass. Glass has higher heat capacity than PC and acrylic and so it has the colder touch, but how about when you compare it with a plastic such as PP. base on the literature, PP has higher heat capacity than glass but it does not hace a cold touch.

 

so, what are the main reason for the cold touch of glass? if we want to have a plastic to have the same cold touch, what parameters or properties of the plastic should change?

[StringJunky]

Glass has thermal conductivity 2 to 3 times higher than typical plastics, so, your assumption that it is very low is where you are going wrong.

 

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

[wayne_m]

There's heat capacity and there's heat conductivity.

A high capacity material can feel warmer to the touch if its conductivity is low, because even though it will absorb more heat, it will do it more gradually than a lower capacity material that can transfer the heat away from the point of contact more efficiently.

That is why a chunk of cold lead lead wrapped in a towel will feel warmer than a glass of water of the same temperature. The lead will eventually absorb more energy, but the glass will carry the heat away from your hand relatively rapidly.

The same thing happens with a wooden tabletop or chair vs a steel surface. The wood, being more massive, will hold more heat than the thin metal, yet it feels warmer - initially, at least. After prolonged contact, the steel will have absorbed all the heat it can, and after the same time in contact, it will feel warmer than the wood, which is still absorbing and diffusing heat through its mass. Of course, the steel will be cooling from the other side, so once the wood has had time to absorb enough heat, it will feel warmer than the steel again, since it is a better insulator against the heat loss to the air.

Edited September 28, 2016 by wayne_m

[StringJunky]

 

 

There's heat capacity and there's heat conductivity.

A high capacity material can feel warmer to the touch if its conductivity is low, because even though it will absorb more heat, it will do it more gradually than a lower capacity material that can transfer the heat away from the point of contact more efficiently.

That is why a chunk of cold lead lead wrapped in a towel will feel warmer than a glass of water of the same temperature. The lead will eventually absorb more energy, but the glass will carry the heat away from your hand relatively rapidly.

The same thing happens with a wooden tabletop or chair vs a steel surface. The wood, being more massive, will hold more heat than the thin metal, yet it feels warmer - initially, at least. After prolonged contact, the steel will have absorbed all the heat it can, and after the same time in contact, it will feel warmer than the wood, which is still absorbing and diffusing heat through its mass. Of course, the steel will be cooling from the other side, so once the wood has had time to absorb enough heat, it will feel warmer than the steel again, since it is a better insulator against the heat loss to the air.

All that doesn't matter with respect to your OP. Relative heat conductivity is enough to explain why glass feels colder than plastic, as evidenced by my link.

Edited September 28, 2016 by StringJunky