Cels Forum

     Leather Art Portfolios will work.  However, the main concern 
when purchasing a "portfolio" is 
  1. The size of the pages (cels won't fit in 8.5" x 11" pockets)
  2. What the clear pages are made out of.
  3. Are the pages sealed on all 3 sides (cels are less likely to fall out)   
As Jotaru mentioned, you should try to get a portfolio that 
has the clear pages made out of Polypropylene, not regular plastic.  
From my understanding, Polypropylene doesn't "stick" to the 
cels.  What I mean by "stick" is that sometimes when plastics come 
in contact with a cel, there may form a spot where that looks "wet", 
probably caused by the chemicals of the plastics.  This also happens 
with glossy photographs or slides.
     Mylar, well, that might work (I don't use it though), although 
I think polypropylene might be better.
     I don't know if this is necessary, but you might want to insert a 
thin piece of museumboard or other acid free material behind each cel so 
they don't flex as much when you flip through the pages.  
     I know that Itoya makes several portfolios with polypropylene 
pages.  Try checking your local art store or art/architecture supply 
store for them.  

        Chad Kawakami