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An invaluable piece of kit. Folding water bag.

This lives in my bag and has proven use full on numerous occasions. Holds 4 litres of water or air for that matter.

Makes a great pillow at night.  Fantastic for acting as a reserve water tank for hand washing or extinguisher of fires.

The opening is wide enough and fits msr water filters. There is also a screw on adjustable nozzle.

Good job.