We're pleased to offer you the ultimate hydration system. Made by Source®, our custom-made, premium bladders use patented anti-bacterial technology, and Glass-like™ liner, so that you get a product that gives great tasting drinks and long life. Plus, we've added our own specifications to make this into the hydration system that best does the jobs that we know our customers will be doing. Special standard features include dual fill options (wide-mouth end opening for stream filling and drying -- plus screw cap) and a high quality weave covered insulated drink tube. Also, the 2 Liter fits all packs, and is recommended for the X1 pack.