# Thermal conductivity

1. Mar 2, 2012

### sasuke07

1. The problem statement, all variables and given/known data
So you have a fridge, the walls of the fridge are made of aluminum, plastic and insulation. Which is the most relevent and why for the fridge.

2. Relevant equations
Thermal conductivity of aluminum=250
Plastic=.03
insulation=0.035 - 0.16

3. The attempt at a solution
I thought by just common sense to be insluation because insulation is mainly used to keep heat either in or out. But i don't know how to describe it in a scientific way? help.

2. Mar 2, 2012

### Staff: Mentor

Last edited: Mar 2, 2012
3. Mar 2, 2012

### sasuke07

Thanks, but i had already found the thermal conductivity of all 3 of the materials. Im just having trouble articluating why insulation is more important than say plastic, if they have a similar thermal conductivity.

4. Mar 2, 2012

### Staff: Mentor

Insulation foam is generally not a very robust surface, and a fridge made of nothing but insulation foam will not please fastidious housewives!

5. Mar 2, 2012

### sasuke07

lol, thats funny, But in terms of thermal conductiviy alone, would insulation be the most important, would plastic be just as good if its thermal conductiviy were similar?

6. Mar 2, 2012

### LawrenceC

When you build any large product, weight is a concern. The density of plastic is roughly the same as water. The density of a foam insulating material is significantly less. Refrigerators are quite heavy objects. If plastic were used instead of a low density foam, the weight would be significantly more.

7. Mar 2, 2012

### Staff: Mentor

Foam is cheaper to manufacture than plastic.