DOUBLE WALL INSULATION. The inner and outer walls are separately molded and printed, then welded together to provide a layer of insulation between liquid and environment. Like a stainless steel bottle double wall insulation really works! PRIMALOFTR BRANDED INSULATION Just hold this bottle in your hand, and you can feel it warm up. That is the body heat from your hand being reflected back from the bottle to your skin. Hows that for effective! We staple a sample of Primaloft to every bottle hangtag so people can feel the quality of the insulation for themselves. You cant see the liquid inside,but the insulation is fantastic. POLYPROPYLENE BOTTLE. PP bottles have superior clarity and lighter weight than standard LDPE bottles. They are very resilient and dishwasher safe. We utilize variable wall thickness manufacturing to make sure this PP bottle is easy to squeeze, no matter the hand size. Like all Hydrapak bottles, they are BPA and Phthalate free. BIG GULP VALVE. Our new TPE poppet is soft on the teeth, a snap to use, and delivers the highest flow of any bottle we know.