Okay, this isn't comprehensive, but it's more comprehensive 
than most places on the subject, I think. Please feel free 
to correct/add something if I don't mention it here. (Remove 
"nospam." from my address to contact me directly.)


I've done more surfing with my last Talas order, and here 
are more links with notes on prices based on a common 
denominating size (about 11x14 inches). I've broken up
the links based on MATERIAL (polyethylene, polypropylene, 
and Mylar D polyester). 

While all are fine archival materials, Mylar D (just a 
brand for a kind of polyester) is supposed to be the best 
archival plastic - also the most expensive. Polypropylene 
is then standard, with polyethylene after that (supposedly 
only slightly less stable than polypro - I'm no chemist, 
but both polypro and polyeth is fine for general not-too-
long-term archiving).

From my previous posts you'll know that I bought 3mil thickness
Mylar bags - these are VERY thick and stiff and will NOT lie 
flat even with a good crease. I personally don't mind because
I like the stiffness. However, I wouldn't recommend getting 
anything thicker than 3mil because of this, unless you plan
on cutting the bags to size. This might not apply to polypro
or polyeth bags since I'm not sure how stiff they are per 
mil thickness (I will be buying more, though).

Note on backing paper: This is optional. I choose to back 
my cels with archival buffered tissue (there's an article 
recommending backing tissue for Mylar bags), but it's 
ultimately your choice (some people back with rice paper or 
glassine, or none at all). Either way, any backing material 
should be acid-free, from most sources. I haven't read 
anything specific about buffered backing for cels, though.

Cel books: what we think of as celbooks are more commonly 
sold as archival scrapbooks and albums. Think general. As 
long as it's acid-free with archival pages (i.e. polypro 
or polyeth), it should be fine.