Nalgene Encapsul Big Bore 1.5L
Here's what other sites are saying:
The Nalgene Encapsul Bladder is produced using only "saturated" polymers. It's high strength is created by blending high-modulus stiff material with low-modulus elastic material to create an energy absorbing strength. Super clean polyethylene encapsulates a flexible core of TPE. Rapid fill cap has 63mm opening.