I've never heard of the term "uncertified container" does anyone have any links to info on this? I did a google search and found nothing. They seem to be at least 4 times thicker than a regular 2 liter bottle, same with the screw on cap. #1 plastic resin code which is used for most beverages. I'm positive if I were to fill it with soda and shake it that it would hold, hopefully someone that has seen them before can comment on this, I really don't know much about the subject. I'm extremely confident they will hold, I'll be sure to post either way. I appreciate the tip beerman!