Re: What is Sarran Wrap made of and Why does it cling to itself so well?

Hi Kevin,

Before you asked this question, I believed Saran wrap (or Glad wrap, as 
it's known here in Australia) was made of polyethylene.  But after a little 
research on the Web, I can now tell you that it is a co-polymer.  That is, 
it is made of two different types of plastics mixed together.

The names of these plastics are Polyvinylidene Chloride, abbreviated to 
PVDC (87%), and Polyvinyl Chloride, PVC (13%).  PVC is also used a lot for 
things such as drainage pipes and electrical insulation.

Now, the second part of your question - why does it stick to itself?

This is caused by electrostatic attraction.  Have your ever done a static 
electricty experiment, such as rubbing a balloon against your hair and 
causing your hair to be attracted towards the balloon (if not, try it - 
it's fun!)  The same principle applies to Saran wrap.  It is 
electrostatically charged, in other words, parts of it have a positive 
charge, and other parts have a negative charge.  The postively charged bits 
attract the negatively charged bits, causing it to stick together when it 
touches itself.  Pretty clever, huh!

You can check out these references if you want to know a bit more:

http://www.britannica.com (search for 
'polymers')

http://inventors.about.com (search 
for 'saran wrap')

http://www.dow.com/saran

I hope this answer has satisfied your curiosity!

Jonathan Feldman
University of Technology, Sydney
dr_chemistry@mad.scientist.com