Reliance Products Green Glacier 2.5 gallon Insulated Water container utilizes a NATURAL straw insulator that has been used for centuries from Roman ice houses to modern day barns. By doing away with chemical foam insulation we are reducing the environmental impact to manufacture an insulated water bottle, and using a replenishable resource that insulates better. The 24oz (710 ml) Green Glacier Insulated Water is made with a BPA Free inner casing. The exterior casing is made from tough aircraft windshield grade plastics. The unique cap design allows you to drink from either the smaller cap opening or larger neck opening (can easily add ice & clean). The cap also features a dual locking mechanism. First, it locks and seals liquid in when closed. Second, it locks in the open position so it doesn"t interfere when you drink.