The place to get packing cubes is eBags. I recommend their own eBags brand, much less expensive and just as good as the Eagle brand.
Their prices are also better the Eagle folders, eBags does not have their own brand for those.
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thank you for the info!!

since you use them, do you recommend one size cube over the other? It sort of seems the large size is a bit of a waste, since you can almost fit too much in there, knim? What about the folders - there's a couple sizes, correct? I assume at times you use all 3 sizes of cubes for different needs, but just wondering if you 'never' use that largest size.