Platypus Big Zip SL 2.0L Reservoir - 70 oz.

One of the reasons that I purchased this product was due to its advertised weight of 4 ounces - otherwise, if it were heavier, I would have simply used another brand. [After all, 4 ounces is a quarter-pound. ;)]
Even though REI lists the weight as "Average Weight," the manufacturer of this product insists on the packaging that it weighs 4 ounces. And I have good reason to believe that this isn't one of those "average weight" matters.
The bladder, hose, bite valve (indeed all the components required for proper use) should weigh 4 ounces as advertised. It actually weighs 5.55 ounces. That is significantly inaccurate. I was displeased when I weighed it and discovered it to be an ounce and a half heavier than advertised. I think that's about 28% off the mark.
[Note: The hose clip can be removed to reduce the weight by 0.2 oz. The blue-slider closure at the top must also be removed for the weight to be accurate (4 ounces) -- though this is not mentioned anywhere on the packaging (...) and would significantly deminish the product's efficiency/integrity.]
I will, however, recommend the Platypus Big Zip SL based upon its features/functionality, but not without warning (for those it may concern) regarding the inaccuracy of the weight.