What kind of press will run pre-made poly envelope mailers?

I'm looking to find out what kind of press will run a pre-made polyethylene mailer envelope, plastic bubble mailers, or resealable zipper pouches. I know you can run these on a silk screen machine for single color, but how are these companies like 4over and uprinting doing these short run full color mailers up to 15x19 sizes. Is it a UV inkjet, or dye inkjet of some sort? There are other companies that are also marketing post-production printing of these items as well, but I can't find out what kind of press will do this. Toner based machines seem to be too hot to run this stuff unless it's polyester based.

I can find plenty of memjet printers that will run uncoated stocks and even corrugate material, but I want something that will print on the plastic bags without needing to be converted after.