The bag is stainless steel (no coating, just steel) with a hook and loop closure, backed with a tight weave webbing.
go to http://www.simpleoutdoorstore.com/outsak.html for detailed info about the differences between the UL and Spectrum bags. Spectrum bags are much bigger.
The closure of these bags has never been the issue as animals will always go straight for the food. We've field tested the bags thoroughly, and have been for almost 4 years. Animals don't use closures. They try to chew trough the stainless steel and they can't do it.
Please remember, the info on the site is not accurate for the UL and Micro we are selling. All of the new info has been posted previously.
We have some instructional videos at http://www.simpleoutdoorstore.com/videos.html
Thanks for your interest. I hope this was helpful.