Endlessly refillable with tap water, dishwasher safe (up to 65 °C), BPA- and phthalate-free, and lightweight for on the go.  
The opening has a certain diameter to ensure optimal water flow and ease of drinking (true story). Or the unique, award-winning three-part design that makes your Dopper easy to fill, easy to take apart for cleaning, and turns the top half of the bottle into a cup.