From: poutnik4nntp@gmail.com   
      
   Dne 12/05/2016 v 00:59 Bret Cahill napsal(a):   
      
   >   
   > Actually I'm looking for a thin flexible elastic film that has low   
   permeability to gas.   
   >   
   > Mylar is very impermeable but polyethylene terephthalate or BoPET has a   
   yield strain of only 5%.   
   >   
   > In contrast butyl rubber is an order of magnitude stretchier than Mylar but   
   gas diffuses through butyl rubber an order of magnitude faster than Mylar, 2   
   orders if the Mylar is aluminized.   
   >   
   > Put other polymers and elastomers on the permeability v elasticity curve and   
   the general trend is stretchy = permeability, however, there are a few   
   outliers.   
   >   
   > One of interest is the old Saran cling wrap, polyvinylidene chloride:  With   
   an ultimate yield strain of 20% it is 4X stretchier than Mylar yet has a   
   permeability an order of magnitude lower than Mylar.   
   >   
   >   
   What about the question, how the permeability   
   changes with stretching ( not elasticity ) ?   
      
   As I suppose the permeability is measured at rest state,   
   but the stretching may significantly impact permeability.   
      
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   Poutnik ( The Pilgrim, Der Wanderer )   
   Knowledge makes great men humble, but small men arrogant.   
      
   --- SoupGate-Win32 v1.05   
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