Mylar D's are GREAT. I've been using them for 5
years and they have kept my collection up
nicely. However, I would strongly suggest
backing your cels with acid-free paper when
using these bags. Over time the paint may
adhere to the bag itself, which would make a
horrible mess of your cel.
I've never had the paper stick to the cel,
except statically, which is easy to remove.