MadSci Network: Physics
Query:

Re: Insulating properties of bubble wrap and aluminium foil

Date: Wed Nov 11 12:00:09 2009
Posted By: Jay Shapiro, Staff, Engineering, TA Aerospace
Area of science: Physics
ID: 1255723727.Ph
Message:

QUESTION:
I have a question about insulation and bubble foil:
When combining Aluminium foil and bubble wrap does it matter what order these materials are in?

For example would a sheet of insulation with two sheets of bubble wrap in between two sheets of alu foil have the same insulating characteristics as one sheet of bubble wrap between two sheets of alu foil with the second sheet of bubble wrap next to the inside sheet of foil? So what we have is four layers (foil-bubble-bubble-foil) on the one sheet and four layers (foil-bubble-foil-bubble) on the second sheet. Same or different?

I need to send some food through the post packaged with an ice pack and want it to stay chilled for at least 48 hours.

Thanks and hope you can help.

Regards
David

Hi David,

To achieve the highest insulation value ( "R" value) for your wrapping, the layers should alternate between the bubble wrap and foil. I found some values of R for several combinations described below:

RSI 0.26 (R 1.5) where the bubble layer is between two layers of foil without air spaces in front of the foil.

RSI 0.53 (R 3) where the bubble layer is between two layers of foil with only one air space in front of the interior facing foil.

RSI 0.62 (R 3.5) where the bubble layer is between two layers of foil with air spaces in front of the foils.

RSI 0.62 (R 3.5) where the foil layer is between two clear layers of bubbles acting as air spaces

Even the best combination cited above (R3.5) is not a great insulation.

Bubble wrap with the smallest size bubbles would be the best, based on the overall thickness of the wrapping. With larger bubbles, more air is allowed to circulate within each bubble. This circulation reduces the insulation properties by conducting more heat through convection.

I have a possible alternative solution: Seal your food in an airtight bag. Place it in a box (as large as practical). Fill the box with a spray urethane foam (available at hardware stores. Make sure that the foam forms the thickest layer possible around all surfaces of the food package. That is, try to center the package inside of the box so that there will be no thin spaces.

Notes of caution:
1) Be aware of how much the foam will expand when applied. This expansion value will be stated on the can.
2) Wear disposable gloves when using the foam because it can be sticky and nasty until it cures.

Though a little more trouble, the foam method can give you an effective R value of up to 7 per inch of thickness, compared to the maximum R3.5 with the bubble wrap.

Good Luck!

Jay Shapiro


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