If you look at older Bubble Wrap, sometimes you will find that it is 
either sticky or has picked up a layer of dust that can't be brushed 
away.  Even though Bubble Wrap is generally made of polyethylene, and, 
many stable products are made from polyethylene or other polyolefins, 
some of these polymers have plasticizers added to the plastic to make 
the product workable during manufacture, use or both.  

This may not be the classic case of "oily" di butyl phthalate in "hard" 
poly vinyl chloride (PVC) vinyl, but it is the same sort of problem.  
Oily "sticky" stuff, added to make a material more pliable (deformable), 
will exude from the surface of the plastic over time, as the mixture 
becomes less stable or properties of components change.  In the case of 
the bubbles, the "sticky stuff" usually transfers to the things it's 
touching.   When the part(s) touching are not uniform, a pattern can be 
seen where they did, and did not, touch.  If the other side of  Bubble 
Wrap was touching, and it was wrinkled, that wrinkle pattern might also 
be seen.  The pattern can be either the plasticizer or dust sticking to 
the "sticky" stuff.  In the case of varnish over a painted surface, the 
polymer of the varnish may absorb the plasticizer.

Bubble Wrap is made by many companies.  The competition is based on 
price.  Thus, the cost of raw materials is important to the 
manufacturers.  The use of non-virgin polyolefins might be found in many 
Bubble Wraps.  In general, non-virgin plastics are stiffer than those 
"made for the application" plastics, and require the use of plasticizers 
to make them softer and usable.  In general, the plasticizer is less 
expensive than the polymer.    

I break this rule when necessary, but the instructors in the packing 
courses I attended (many years ago), taught that the first layer is 
always paper.  I generally use acid-free glassine, but then I'm often 
working with works on paper or photographs.

Tim Vitale
Paper, Photographs &
Electronic Media Conservator
Film Migration to Digital Format
Digital Imaging & Facsimiles
Preservation & Imaging Consulting
Preservation Associates
1500 Park Avenue
Suite 132
Emeryville, CA 94608

510-594-8277
510-594-8799 fax  

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